By Fergus Walsh
Medical correspondent, BBC News
Two British couples have donated and received kidneys from each other in the first paired transplants in the UK.
Roma Horrell says the operation has transformed her life
They are part of a new scheme aimed at increasing the number of donor organs.
Peter Horrell, from Cambridgeshire, donated one of his kidneys to a man from Lothian, while the man's wife gave a kidney to Mr Horrell's wife Roma.
Mrs Horrell, whose husband's kidney was not compatible for her, and the man benefited from laws introduced in 2006 allowing live donations from strangers.
Until the new laws came in last September, patients could receive a live transplant only from a relative or close friend.
Mrs Horrell, who had her operation three months ago, said it had transformed her life.
"I used to do home dialysis twice a day so it was quite a burden," she said. "Plus I got crippling gout, one of the side-effects of my kidney failure.
"Sometimes I was barely able to walk or bend down. Now I feel really well, it's given me my freedom back."
Mr Horrell wanted to donate his kidney to his wife but he was not a compatible donor, and says this is the next best thing.
"As far as I was concerned I was helping Roma in this way. We're also very grateful to the woman in Scotland who gave a kidney to Roma. Indeed, everyone has benefited," he said.
One kidney was flown down from Scotland
The transplants involved four carefully co-ordinated operations at Addenbrooke's Hospital, in Cambridge, and at Edinburgh Royal Infirmary.
Mr Horrell's kidney was packed in an ice-cold solution and sealed inside a plastic bag.
It was then driven to a local airport and flown to Edinburgh. The reverse happened with the donor kidney for Mrs Horrell.
The transplant surgery in Cambridge and Edinburgh would have been illegal until 1 September 2006 when the law was changed.
It is hoped the new rules will increase the number of organs available.
Professor Andrew Bradley, a surgeon at Addenbrooke's Hospital, carried out one of the transplants.
He said other countries had used paired transplantation for years.
"It's a sensible step forward which will hopefully help more people get off the waiting list," he said.
"At the moment people spend on average three or four years waiting for a kidney and many never get a transplant."
The Scottish couple involved want to remain anonymous, but Mr and Mrs Horrell hope by publicising their involvement it may encourage other couples - where one needs a new kidney - to go on a special paired transplant register.
There are currently 31 couples on the list.
About 6,500 people are waiting for a new kidney in the UK and last year about 2,000 kidney transplants were performed.