(FORTUNE Magazine) – Companies have tried all sorts of things to improve corporate life for minority employees. Many efforts fail, but one approach has proved so successful that it should be a staple at every concerned firm: mentoring. Why are mentors effective? For starters, employees of color have a crying need for the guidance senior people can provide. A study by Korn/Ferry International and the Columbia Business School found that 80% of high-level minority executives lack formal mentors to help chart their careers; nearly a third don't even have informal guides--and these are minority executives who have "made it."

To find out how mentoring can be effective in retaining and promoting minorities, we got to know Pat Carmichael at banking giant J.P. Morgan Chase. J.P. Morgan and Chase both had mentoring programs before their merger, and now every business unit at the combined company sponsors several. Carmichael has mentored hundreds, both formally and informally, over her 30-year banking career. Currently she boasts a roster of about ten "mentees"--people she talks to at least once a month. She's worked with people of all races--including whites. One of her current charges, John Imperiale, is a 25-year-old white assistant branch manager from Glendale, N.Y.

We'll get back to Imperiale in a moment. First, a few reasons Carmichael, 48, is such a terrific mentor. For one, she has an important job--she is a senior vice president overseeing Chase branches in Queens and Long Island. That alone makes her a role model. And she has three decades of experience to draw on when she counsels minorities. Carmichael advises them to ask for tough assignments--and feedback. "Minority employees have to take the initiative and say to their bosses, 'What do I need to do to grow?'" she says. All too often, Carmichael says, bosses hesitate to give constructive criticism for fear of appearing biased.

Carmichael is also a consummate networker, introducing her proteges to key executives--especially other minorities. "Pat has increased my access to other African Americans in senior roles such that I don't ever need to make a cold call," says Dinah Moore, a 43-year-old senior vice president in one of the bank's technology groups. How powerful has mentoring been for Moore? "[It's] one of the components that has kept me at Chase," she says.

Carmichael started as a teller at Chemical Bank (later purchased by Chase) in the early 1970s. It's no surprise, given the era, that her own mentors were white males. She speaks fondly of Bob Como, now a vice president in J.P. Morgan Chase's middle-markets group. When she started as Como's deputy, Carmichael was "a shy, skinny kid" who sat in the back during meetings. Como pushed her to voice her ideas and lead discussions.

That's part of the reason Carmichael now mentors a number of nonminorities, including Imperiale. Her motives aren't entirely colorblind. "My hope is that the exposure John has to me will give him insights when he's managing a diverse group of employees," she says. But there's more to the relationship than race: It was Carmichael who encouraged Imperiale--a quiet young man who feels most comfortable analyzing numbers--to broaden his experience with a stint managing a bank branch.

For all her efforts to be inclusive, Carmichael still feels a special obligation toward minorities. "When you go to meetings and don't see people who look like you, you start to wonder why that is," she says. ''And how do I get involved so that when I leave, that isn't the case?" Thanks to her work--and the bank's support--it's changing already.