(FORTUNE) -- So there you are, Mr. or Ms. Hiring Manager, interviewing a candidate for an important job in your organization. The person sitting across the desk from you is bright, articulate, accomplished.

But if you hire him, is he likely to pursue his mission at your company with true passion - the kind of go-the-extra-mile energy and dedication that leads to great things? Or is his apparent zeal for the task ahead all sizzle and no steak? Hard to tell, isn't it?

After all, almost anyone can come across in a job interview as a world-class go-getter. So how do you distinguish true passion (which can't be faked) from enthusiasm (which easily can)?

"Enthusiasm can be a false signal, and interviewers are often misled by it," notes hiring guru Lou Adler, CEO of the Adler Group, a consulting and training firm that has given hiring lessons to managers at dozens of Fortune 500 companies. Adler is also the author of a bestseller called Hire with Your Head (Wiley, $34.95). "You don't want just any passionate person. You want someone who is going to be passionate about this job."

To gauge that, Adler recommends digging deeply into a candidate's work history. "You need to take the time to do a detailed, job-by-job review. Where did this person excel in the past? What specific achievements got recognized and rewarded? Why did she get promoted? Which job or jobs really gave him a chance to shine? This will show you pretty clearly what the candidate is passionate about. Then you can assess whether her passions match the job you're trying to fill."

Someone with a phenomenal talent for wooing new clients, for example, may not be the right fit for a sales-manager position that will put him behind a desk managing other salespeople without ever meeting a customer.

Likewise, someone whose success so far has come from passionately pursuing engineering solutions on her own may not thrive in a position that requires constant teamwork.

"The better you understand both the job itself and the person you're considering for it, the more likely you are to get someone who can direct his or her passion where you need it to go," Adler says.

Beyond that, there are some interview questions that should help you determine whether a candidate really has fire in the belly. David Sanford, now an executive vice president at recruiting and staffing firm Winter, Wyman & Co, spent the first part of his career as a human resources manager at Wang Laboratories, Bank of Boston, and Doubleday, so he's looked at this from both sides.

"I always think that when companies talk about passion, one thing they mean is, a willingness to take risks," Sanford says. "So one question I ask candidates is, 'Tell me about some of the risks you've taken and how they turned out.' A person who has never taken a risk is probably not who you're looking for."

He adds that "passion really comes down to confidence and courage, including a willingness to push back and take an unpopular position if you really believe in it."

How can an interviewer measure that? "One test is, will this candidate debate with me?," says Sanford. "Sometimes during our conversation I'll roll out an opinion or an idea that I know is way out of left field, just to see if the candidate is willing to argue - politely, of course, but with conviction."

Sanford also pays close attention to the questions candidates ask. "Passionate people will ask you a question and then, based on your answer to that one, ask you another one," he says. "They're not sticking to a script they prepared beforehand, they're following one idea to another idea to another idea with genuine spontaneous curiosity. That shows passion."

Another tip-off: "I ask people what they are passionate about outside of work. Someone whose eyes light up when they talk about a sport or a charity or whatever it is they do in their spare time - that is someone who will probably be passionate on the job too. People don't switch their passion off when they walk into work in the morning. It carries over. By contrast, someone who's just going through the motions with no special passion outside of work will probably be the same way in the office."

According to Sanford, passion isn't all that hard to spot - if you really try. Indeed, he believes companies that can't seem to bring many passionate people on board have only themselves to blame.

"Too many employers pay lip service to the idea of passion but in fact they want cookie-cutter thinking, which is why they end up with cookie-cutter hires. They want everyone to stay in his or her neat little box," he says.

"I've seen it time and time again," Sanford continues. "Hiring managers will opt for the 'safe' candidate rather than a more provocative one - and then they're disappointed a year later when the person hasn't stepped up and produced fantastic results."

A word to the wise...

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