Doctors in Glasgow have injected stem cells into the brain of a stroke patient in an effort to find a new treatment for the condition.
The elderly man is the first person in the world to receive this treatment - the start of a regulated trial at Southern General Hospital.
He was given very low doses over the weekend and has since been discharged - and his doctors say he is doing well.
Critics object as brain cells from foetuses were used to create the cells.
The patient received a very low dose of stem cells in an initial trial to assess the safety of the procedure.
Over the next year, up to 12 more patients will be given progressively higher doses - again primarily to assess safety - but doctors will be looking closely to see if the stem cells have begun to repair their brains and if their condition has improved.
The company making the stem cells says the trial has ethical approval from the medicine's regulator.
It also points out that foetuses were used in the very early stages of the research and are now no longer used.
Professor Keith Muir, a neuroscientist at Glasgow University and a consultant neurologist at Southern General Hospital, said if the trials went well it would lead to more detailed research.
"We hope that in the future it will lead to larger studies to determine the effectiveness of stem cells on the disabilities that result from strokes," he said.
The first group of patients to receive the treatment will be men over 60 who have shown little or no improvement in their condition over a number of years.
It is an ideal group to assess the safety of the procedure - doctors will be keen to know first of all that the treatment makes them no worse.
But having such a precisely defined group will enable doctors and scientists to compare like with like if they notice any improvement - even in these early stages.
If these trials show promise, doctors plan larger trials on a more varied group of patients. The earliest this could begin is in two years' time.
There will be more focus on assessing the effectiveness, if any, of the stem cell treatment and on which groups it works best.
Patients will be monitored for two years, followed by longer term procedures after that.
The announcement from the Glasgow team comes a few weeks after the US firm Geron said it had begun its clinical trials on a patient to develop a treatment for paralysis.
The development of stem cell treatments is still at a research stage and it is likely to be many years before becoming widely available.
But new potential treatments are now beginning to make their way from the scientist's laboratory into the doctor's clinic.
Strokes kill around 67,000 people in the UK every year, according to the Stroke Association.
The charity says it is the third most common cause of death in England and Wales after heart disease and cancer.
The disabilities suffered by patients also have a greater impact than any other chronic disease, it adds.
The trial is being carried out with ReNeuron Group plc which was given approval from the UK Medicines and Healthcare Products Regulatory Agency (MHRA) in January last year.
The company's Chief Executive Officer Michael Hunt said: "The initiation of the clinical trial is a major and hard-won milestone in the development of therapies to address the severely disabling effects of stroke."