But medical authorities in the US have concurred that the surgical transplantation of a full human face is now technically possible. What's more, two highly respected medical institutions, only a few hundred kilometres apart from each other, have been given clearance to perform the controversial medical procedure.

Doctors at the Cleveland Clinic Foundation, in Ohio, and the Medical School at the University of Louisville in Kentucky are now both quietly screening possible candidates to receive the world's first face transplant.

Such an operation, when finally scheduled, is expected to take from 12 to 16 hours. That's the estimated time it will probably take for a team of expert surgeons and medical technicians to disconnect the hundreds of tiny veins, arteries, tissues and muscles that connect the human face to the skull of a cadaver ... and then repeat the process in reverse, restitching the face - from hairline to jaw line, and from ear to ear, including the mouth, lips, nose, eyebrows and eye lids - to the living patient's skull.

A recent New York Times report suggests that Maria Siemionow of the Cleveland Clinic will likely be the doctor to lead a team of medical experts in performing the world's first face transplant. The Polish-born, US-trained surgeon is the director of plastic surgery research at the hospital. At age 55, Dr Siemionow has been involved in transplant surgery for about 30 years and has been researching the possibility of face transplants for half that period.

However, when questioned about having a patient ready to undergo a face transplant, Cleveland Clinic spokeswoman Eileen Sheil told the South China Morning Post that no such candidates had been yet identified, and no timeline had yet been set for the pioneering procedure.

Meanwhile, at the University of Louisville's School of Medicine in Kentucky, John Barker has a team of his own that is also preparing to perform a face transplant, although he won't predict when his team will carry out the procedure. Dr Barker, director of plastic surgery research at the university, where the first hand transplant in the US took place six years ago, is adamant however that 'face transplants will be done'.

Unlike transplants of solid organs such as hearts or kidneys, which have long become routine, hand transplants and face transplants require the transplantation of multiple types of tissue, including skin. And this is what has held back the prospect of face transplants. But Dr Barker said that through initial research 'we found a certain cocktail of drugs is effective in stopping rejection of skin'.

'Technically, a face transplant could have been done 10 years ago. There is a great need. There may be ethical issues, but there comes a point where you've just got to do it.'

Asked when such an operation might take place, Dr Barker told reporters: 'We'd rather not say. The minute you put a date or a time - then all of a sudden, it's a race.'

While medical specialists argue the pros and cons of a face transplant, they all agree on one thing: that selecting the proper patient can make the difference between surgical success and failure. Because of the need to take immunosuppressants for life, cancer patients would not be eligible, because such suppressants would lower their immunity against future tumours.

Ideally, candidates should be relatively young. Most important, the best patient would have a strong sense of confidence and self worth. One possibly ideal candidate is Jacqueline Saburido. In 1999, the then 20-year-old was a student at the University of Texas. The car she was riding in was hit head-on by a drunk driver.

Two other students in her car were killed. And by the time rescuers pulled Ms Saburido from the burning vehicle, her face - including her lips, ears and nose - had burned away. Aside from losing her face, she received burns to 60 per cent of her body. Her hands were so badly burned that her fingers had to be amputated. The drunken driver, who was uninjured, received a sentence of seven years in prison and was fined US$20,000.

Since the accident, Ms Saburido has undergone more than 40 operations, but has bravely become a spokesperson against driving and drinking, appearing on posters and television.

Today, she lives with her father, who is now her full-time care-giver, in Kentucky, having moved to Louisville to be near a team of doctors who are still trying to help her.

'My life,' she says, 'completely, completely, completely changed' in the accident.

In addition to reconstructing her face, she hopes to rebuild her life. She hopes to marry one day and to have children. 'I hope I can do [so] soon,' she told a Texas newspaper. 'Because life is now.'

In fact, human faces have been replaced before. In 1994, a young child in India lost her face and scalp in a threshing machine accident. Her parents raced to hospital with her face in a plastic bag and a surgeon managed to reconnect the arteries and replant the skin. There have been similar successes in Australia and the US.

The chief medical difficulty with transplanting the face of one person to another, aside from the surgical challenge itself, is that the body's own immune system will immediately fight to reject the new skin as an invader.

Some doctors have suggested that, aside from the functional recovery of the skin graft, the side effects of a lifetime of taking immunosuppression drugs are still unknown.

For that reason, European medical experts have backed away from the procedure, claiming that the radical operation is simply too risky to outweigh the possible benefits for patients whose lives are not genuinely endangered. Aside from the risk of the surgery, face transplant patients would have to follow a strict regime of anti-rejection drugs throughout their lives, as well as follow a special diet.

But Peter Pang Chi-wang, a specialist in plastic surgery at the Prince of Wales Hospital, is supportive of the concept. 'A facial transplant is definitely feasible and is technically quite easy to perform,' Dr Pang said.

'The surgeons just need to anastomose [connect] four nerves and two vessels in order to have the 'new face' survive and function in the recipient. Recent refinements in the use of immunosuppressants makes rejection much less of a problem.

'I think there are some patients under our everyday care who would benefit from a face transplant. They are people with severely scarred faces, mainly due to burn injuries. No matter how hard we try utilising present-day techniques - for example using skin grafting and free tissue transfer [from the patients themselves] - these patients cannot receive satisfactory results. So a facial transplant apparently is the answer for that.'

Julie Woodley, a British expert in transplant ethics, calculated that about one in five face transplants could be rejected within three years, the estimate being based on the success rate for kidney transplants.

Citing such high risks, Arthur Caplan, chairman of the bio-ethics department at the University of Pennsylvania, said: 'And if the first surgery were to fail? The risks to the patient are staggering. This is a terrible idea that should not be tried.'

However, medical researchers at the University of Louisville are already using a US$2.5 million federal grant to study new ways to reduce or even eliminate the potent blend of immunosuppression drugs now needed after transplant procedures. Researchers have already found that a combination of drugs used for kidney transplants would also work with skin transplants.

Both Ms Woodley and Sir Peter Morris, president of Britain's Royal College of Surgeons, said that supporters of face transplants had not fully considered the psychological impact on the recipient and on the donor family. Ms Woodley said proponents of face transplants had 'glossed over' the possible psychological damage to people receiving face transplants, and to the living relatives of people who had donated their face.

Other medical ethicists continue to ask stark questions: How would donors be located? How would the family of a donor react to seeing the face of a lost loved one on someone else? How would the family of the patient react to seeing a stranger's face on their loved one? And, finally, how would the face transplant patient react psychologically to seeing a strange face in the mirror?

As to the belief that the face of a transplant recipient would be identical to that of the donor, it's a falsehood, based on Hollywood movies. According to Dr Pang: 'Facial transplants only transfer the facial soft tissue, while the bony skeleton is not involved. And studies have been shown that the recipient patient may not have the exact facial features of the donor.'

Dr Barker, whose team includes three bioethicists, concurred, noting that the underlying skeletal structure of each individual differs greatly, and it is the shape of the skull that largely determines what individuals look like. This means that the beneficiary of a face transplant would look much different from that of a deceased donor's face.

Patients who have had their faces destroyed by fire or disease or accidents sweep such academic questions aside, however. There are literally thousands of people worldwide whose faces have been terribly disfigured; they are well aware of the risks but are ready to volunteer.

Christine Piff, founder of the British charity Let's Face It, welcomes the possibility of face transplants. Ms Piff, who suffered from a rare form of face cancer 25 years ago, says: 'There are so many people without faces - I have half a face. But we are all so much more than just a face. If we can donate other organs of the body then why not the face?

'When I first heard of face transplants I was truly horrified. But over the years I've met so many miserably unhappy people. I've changed my mind.

'We don't go out because of the way we look. We're frightened because of how the public stares at us. So disfigured people just shut themselves away. They only leave home at night, with hoods over their faces. For them, face transplants could mean at least a chance at a normal life.'