Confident and educated, Generation X women were supposed to bring fire to the work force. Instead, they're burning out in alarming numbers. Following more than two decades of increases, the labor force participation rate of women began to fall precisely when the first Gen-X women turned 34. In 2004, that number stood at just 53%. With baby boomers nearing retirement, and far fewer Xers than there are boomers, companies are racing to figure out what the big turnoff is.

Changing attitudes are partly to blame. As Charlotte Shelton, a business professor at Rockhurst University in Kansas City, Mo., writes in her new book, The NeXt Revolution, women born between 1964 and 1977 have high expectations about work--a product, she theorizes, of boomer parenting. As evidence, Shelton cites her survey of 1,200 Gen-Xers, which found that respondents valued "interesting work" and "opportunities for learning" over salaries. (Gen-X men show the same traits but drop out much less often.)

Work-life balance is another source of tension. If boomer moms worked, they typically accepted long, set hours "just because [they] were so grateful to have an opportunity to play the game," Shelton says.

In contrast, Gen-X women see family-friendly work policies as a birthright. And yet these policies are still rare. Only 19% of companies surveyed recently by the Society of Human Resource Management offered job sharing. Just 27% allowed parents to bring kids to work in an emergency.

To retain Gen-X women, then, companies should look at job sharing, flex time, even on-site childcare. They should also build "on ramps" for young mothers returning to the work force. Last year, for example, Deloitte & Touche launched a program to let employees take time off (up to five years), so long as they agree to regular training. The cost to Deloitte: $2,500 per employee, a fraction of what the accounting firm would spend to replace the 28 managers who were part of the pilot class.

If employers don't change, they can expect to lose workers like Melissa Slack. After seven years in a corporate job, Slack, now 36, decided that no salary or title was worth the sacrifice. When she found out she was pregnant, she quit. Two years ago, she co-founded Let's Eat, a storefront-cooking franchise in Tampa. This raises an interesting possibility: While Gen-X women may be too demanding (or sensible) to be docile employees, perhaps they're perfectly wired for entrepreneurship.