Six recipients received organs from six donors in operations at the Johns Hopkins Hospital in Maryland.
The procedure was made possible after an altruistic donor – neither a friend nor relative of any of the six patients – was found to match one of them.

Five patients had a willing donor whose kidney was incompatible with theirs, but it did match another in the group.

This meant that suddenly, there were six people who could receive an organ.

The operations were carried out simultaneously to make sure no-one backed out after their loved one had received a kidney.

“All 12 and doing great, the six kidneys are working well,” said Dr Robert Montgomery, director of the transplant centre at the Johns Hopkins hospital.

(emphasis added)

http://news.bbc.co.uk/2/hi/health/7338437.stm

So, let’s break that down. Five people needed kidneys, and had relatives or friends who would donate a kidney, but the kidney did not match. Software figured out that A’s kidney would fit B, B’s would fit C, C would fit D and so on. But to make sure that nobody backed out, they put everybody under the knife, so that nobody would break the chain because their friend now had a kidney…

Wow that’s hardcore. No welching on the deal, you’re all going to put your kidneys on the table – it’s an issue of protocol design….