Johns Hopkins surgeons transplanted a half-dozen kidneys simultaneously, an operation believed to be the first of its kind, hospital officials announced Tuesday.

The transplants conducted Saturday were made possible when a so-called altruistic donor, who was willing to donate to anyone, was found to be a match for one of six transplant candidates. Five of the candidates had a willing donor whose kidney was incompatible with their particular friend or relative, but a match for another of the six.

The 10-hour surgeries used six operating rooms and nine surgical teams.

"All 12 are doing great, the six kidneys are working well," said Dr. Robert Montgomery, director of Hopkins' transplant center and head of the transplant team.

The six-way transplant follows a quintuple transplant performed in 2006 at the hospital and several triple transplants. Last week, doctors at Chicago's Northwestern Memorial Hospital performed simultaneous transplants of four kidneys.

Most kidney transplants use organs taken from people who have died, but doctors prefer organs from live donors because the success rates are higher. The donors and recipients in the six-way transplant were matched using a living-donor system developed at Johns Hopkins.

Montgomery said the surgeries are performed simultaneously to ensure no one backs out after their loved one has received a kidney.

Montgomery has advocated a wider system of connecting altruistic donors, transplant candidates and incompatible but willing donors to increase the number of available organs.

Randy Bolten, whose brother is President Bush's chief of staff, Josh Bolten, was among the donors. He couldn't donate a kidney to his wife, Jeanne Heise, but he was a match for another recipient.

Heise, who has suffered from kidney disease for more than 30 years, was about to go on dialysis when the chain of transplants became possible.

"We want to spread the word about this sort of group surgery and living organ donation," Heise said in a statement issued by the National Kidney Foundation of Northern California.

"The waiting list for a kidney is very long and too many people die while waiting. With this group procedure, more and more people can beat kidney disease and live long productive lives."

The United Network for Organ Sharing knows of no other six-way transplant, spokeswoman Amanda Claggett said. She added that so-called paired donations are still very rare.

More than 252,000 kidney transplants have been performed in the United States since UNOS started keeping data in 1988; 87,000 of the kidneys came from living donors. There have been only 301 transplants performed through so-called paired kidney exchange, including 122 in 2007, Claggett said.

She said more than 75,000 people are waiting for kidney transplants and 4,352 died while waiting for a kidney last year.