NEW YORK — Dr. Diane E. Meier, a geriatrician at Mount Sinai Medical Center in New York, is an expert on end-of-life care. So when her elderly parents needed long-term help at home with bathing, dressing and cooking after her father's stroke, she knew where to find assistance.

It was not through agencies in Manhattan that provide home health aides who are bonded, insured and certified. A year of custodial care from such an agency would cost her family $150,000, and in short order exhaust its savings because aides are not covered by government assistance unless patients are poor or fresh from a hospital stay.

Instead, Meier turned to "a little list" of aides from the so-called gray market, an over-the-back-fence network of women. They are usually untrained, unscreened and unsupervised, but more affordable without an agency's fee, less constrained by regulations and hired through personal recommendation.

With 4.2 million Americans currently older than 85 — a number that is expected to grow 40 percent, to 5.9 million, by 2014, and then accelerate with the baby boom generation — the exploding need for long-term care is remaking the home-care industry, driving more of it underground.

Gray-market hiring, fraught with risks, is a solution that middle-class families are turning to as they face the crushing burden of indefinite home-care expenses. But it is hardly the only one, as businesses rush to meet the needs of these families, the fastest-growing segment of the marketplace, who are intent on keeping their loved ones out of nursing homes.

Traditional agencies like the Visiting Nurse Service, founded to serve the poor with all manner of home health care, are opening divisions geared toward clients who must pay their own way. At VNS, 15 percent of clients pay out of pocket, an 11 percent increase over last year, and aides trained in wound care and vital signs are also learning to interact with doormen, use espresso machines or escort a client to the opera.

At the same time, upscale agencies providing trained aides are proliferating solely for the private-pay market, as are national chains with more modest services — and more reasonable prices. These franchises are intended for today's consumer of home health care who needs simple companionship, reminders to take medication, an escort to doctors' appointments and help in preparing meals.

The largest of these chains, Home Instead, opened in 1994 with six franchises and now has 722. Their 37,000 part-time workers tend to the needs of 43,000 elderly clients. The advantage is a lower hourly fee — say, $15 an hour for nonmedical needs vs. $20 an hour for a trained agency aide — and the disadvantage a scramble to find more skilled help as a patient's health declines.