Imagine needing to buy a new business suit or evening dress, and deciding from home what style, size and color will best suit you. Then heading to the stores to buy it, not really knowing whether the outfit you envision even exists. And, if it does, picture buying it before trying it on to see how it fits.

It's hard to see taking such a leap of faith with an expensive piece of clothing. Yet executives and professionals take similar untested leaps all the time when trying to change careers, according to Herminia Ibarra, author of a book called "Working Identity: Unconventional Strategies for Reinventing Your Career" (HBS Press, 2003).

Just as an unlikely item can fit perfectly while something that looks great on the hanger can disappoint, jobs that appeal to you from the outside can turn out to be poor fits in unexpected ways. Meanwhile, a career that you stumble into can turn out to seem tailor-made to your interests and abilities.

The most common career-change strategy has professionals undergo a battery of tests to inventory their skills and interests, choose a career that appeals based on the results, and then go out and look for a job. Ms. Ibarra equates this prescription with the buy-first-and-try-on-later approach to shopping.

"Those tests can help you only so much, because the job that's really right for you might be one you hadn't thought of, or that you don't even know exists," she says. "You have to assume you don't know everything about yourself and be willing to learn by doing."

Ms. Ibarra, a professor at the French business school INSEAD, spent several years tracking professionals in various fields in several different countries who successfully changed careers. Some made relatively incremental transitions (a white-shoe consultant became a business-development executive at Virgin Group) and others, deeply life-changing ones (a psychiatrist became a Buddhist monk). The common link she discovered was that they all found ways to try on one or even a few new fields before fully committing to anything.

Drawing on her case studies, Ms. Ibarra recommends using any of a variety of methods -- reading, talking with friends and acquaintances, auditing classes, going to conferences, volunteering, even free-lancing or taking interim jobs -- to dabble in new activities. Through these experiments, career changers can gain a new perspective on their interests and abilities and discover jobs they hadn't known about. Eventually, she says, these career changers do commit to a new field, but without having to try to do it in one bold and risky leap, which often backfires.

"I had to learn that changing careers is a process. You have to give yourself permission to enjoy the process rather than dreading the fact that you're going through it," says Bruce Strong, who read Ms. Ibarra's book after leaving Context, a technology firm he co-founded and helped to run for 10 years.

Mr. Strong left Context in the fall of 2001, tired of what he'd been doing and believing he could easily parlay his hands-on tech knowledge into a consulting career. But his first few job interviews were nonstarters. "I was a green banana," who didn't know the industry jargon or understand how consulting services are sold, he says. "I needed to ripen a little."

So he backpedaled and tried a more exploratory approach. He got in touch with clients from Context who had used consultants to find out how and why they used them, and to ask for references to consulting executives who might give him advice.

One consultant told him he had interesting ideas about where technology was heading, but "there was no way to implement what I was talking about, so [the executive] couldn't sell it," says Mr. Strong. "I needed to turn these ideas into a methodology that I could pitch to clients."

He worked on that, but also tried his hand at writing -- submitting articles to the Harvard Business Review and talking to an agent about a book -- figuring that writing might turn into a career path in itself or at least bolster his consulting credentials. And, as he got more involved in the exploration side of his career hunt, he briefly apprenticed with a professional photographer, to see whether he wanted to turn a hobby into a career (he didn't).

Further conversations with consultants and other business professionals helped him to refine his ideas about technology strategy, and through those meetings he eventually landed a few clients. But he sees himself as still trying consulting on, and trying on other things as well, like book writing and teaching. "What's most important is to continue to build intellectual assets," that he can use in a variety of ways, he says.

Mr. Strong used the wealth he had accumulated through Context to fund his search. Stuart Lindenfield, a senior managing consultant in London for Drake Beam Morin, an outplacement-consulting firm, says self-funding this transition with savings or severance isn't uncommon for high-level executives.

But family, mortgage and other obligations can discourage lower-level managers from leaving a job to do full-time career exploration. Ms. Ibarra and others point out that there are several ways to use one job to figure out what your next might be.

Mr. Strong, for example, sees in retrospect how he could have used his old job to facilitate some of the experimenting he did on his own. "I could have started networking with clients, or done some extracurricular or pro bono consulting," he says. "I also could have gone to a Bain or McKinsey [representing Context] to suggest working together and then learn from them along the way."

Mr. Lindenfield points out that a person who has had one career for 10 or 20 years can have a hard time thinking about their abilities and interests outside of the context of that job. "It can be refreshing and liberating for them to do something completely different, because it shows them that they can use their skills in different ways and opens them up to possibilities."

Sometimes the act of trying something new is actually more important that what you try. You gain a fresh perspective you can use to segue to the thing that really suits you.

For example, Nicholas Jacobs, chief executive officer of the Windber Research Institute in Windber, Pa., started out as a high-school music teacher. After 10 years of teaching he wanted out, but when he interviewed for business jobs, "People told me my teaching equates to nothing in business. I had one guy tell me I was worthless," Mr. Jacobs recalls.

"I knew that wasn't true, but I had to get into the business world to see how my skills would [apply] and to know how to talk about them," he says.

At about the same time, a company that sells products that schools use for fund-raising heard about a particularly large fund-raiser he'd led for his marching band and recruited him. It was a brutal job -- he actually earned less money than he had as a teacher -- that lasted only nine months. "But I don't think I could have done the jobs that came later without the time I spent in that one," he says. "It taught me what I had and didn't have."

He wasn't aggressive enough to be a good salesman, but he realized that he did have good people-management skills. "Managing a marching band with 185 students is all about getting people to work together and motivating them to do things they aren't sure they can. It's all about leadership."

He began to understand that what he really wanted to do was use his interpersonal skills to earn a living and "do something that would make an impact." He saw an opening for the director of a regional arts organization and, thinking it was a chance to use his arts background while learning about business, he applied. And got the job.

The organization was struggling with a small membership and weak attendance at events like art exhibitions and music festivals. So he used his understanding of the school system to make his programs for children more attractive to area schools, which raised the organization's profile with parents and teachers. And he used the presentation skills he'd honed as a teacher to talk to more than 150 community groups, like the Kiwanis and Rotary clubs about his programs.

Over the course of four years, the organization grew to 3,000 members from 300, and the parking lots began to fill up at festivals.

More importantly, he'd found a career he could settle into: turning around troubled not-for-profits. He later went on to build up a regional tourist bureau and a hospital.

Ms. Ibarra notes that she's also seen several professionals take what amount to rent-paying jobs to fund their exploration. Some of those people freelance or find a job with fewer responsibilities and shorter hours, so they can have time to volunteer, take classes or try to get a business going.

"It's an incremental step," she says. "The calculation you have to make is: Will this take you on a path that will lead you in a few years to that next thing you want to do?"

In addition to retraining you for something new, school -- a broad program like a master's in business administration, or a single class here and there - can help you to figure out what that new thing might be.

Alison Wagonfeld, now the executive director of Harvard Business School's West Coast research center, knew she wanted to leave investment banking when she returned to school, but that's about all. "It occurred to me when I was applying that the work I liked as an investment banker was taking companies public, which was sort of marketing the companies to investors," she says. So she began taking marketing classes, liked them, and took a few more. After finishing at Harvard, she joined Intuit, the software firm in Mountain View, Calif., to work in product development, launching new online services.

As an example of a less expensive route, Ms. Ibarra points to a stockbroker who audited classes and attended such extracurricular events as mixers and lectures at a local university to figure out what she might want to do after moving on from Wall Street.

This approach to changing careers is "more organic and more the way things actually happen," than taking assessment tests, says Ms. Ibarra. But it isn't a quick or easy fix. This trial-and-error approach can take a few months or, as with Mr. Strong, a few years.

"It's always painful to deal with uncertainty," she says. "But, you really do have to get involved in things and see how you react: When you talk to this person, you get excited, but when you talk to that one, you get that sinking feeling."

She notes, "Everything grows your muscles and the quicker you start, the sooner you get there" -- wherever there may be.