It was driven by for-profit centers that market machines to people with a tremendous sense of claustrophobia and anxiety.

Last year there were 54 for-profit centers in Nassau, an increase from 18 in 1990.

A number of for-profit centers exist, he said, but they are allowed to pay donors only for plasma, the clear part of blood without red cells.

Dr. Salick began opening for-profit centers in 1986 in California, then expanded to Florida.

Physicians working in for-profit medical centers and health maintenance organizations, which provide care on a prepaid system, probably have greater difficulties in providing free care, medical leaders say.

Two-thirds of the 200,000 Americans on dialysis are treated at for-profit centers, which have come to dominate the dialysis industry in the last 25 years.

The researchers found that for every 100 patients treated a year, 21.2 died at for-profit centers, as against 17.1 at nonprofit centers - a 20 percent higher risk of death.

"The vast majority of for-profit centers are operating closer to the 8 percent range," he estimated.

In the last decade, the proportion of for-profit centers has grown.

One proposal is from two women who manufacture kettle drums for symphonies, and another for a for-profit day-care center.