For a medical centre supposed to be at the cutting edge of medical science, Dr Geeta Shroff's Nu Tech Mediworld clinic is a modest edifice. Hidden down an alleyway in one of the seedier residential areas of south Delhi, the little building can be reached only by squeezing past rickshaws and motorbikes. The waiting-room is decorated with yellowing newspaper cuttings about Shroff's work. From time to time, there are power cuts, leaving patients facing the 43C heat.

Not that they care about such discomforts. Patients at Nu Tech Mediworld believe they are going to be cured of major medical traumas using life-transforming embryonic stem cell therapy. The desperately ill started heading to the clinic after a number of Shroff's patients, who had motor neurone disease, broken spines or were paralysed, went public with stories of 'miraculous' improvements in their conditions.

'This feels quite miraculous,' admitted one motor neurone patient who had recently arrived from Australia.

This desperate pilgrimage is not without critics, however. Some doctors say Shroff is treating her patients as human guinea pigs, and question both her ethical and medical standards. Nor are these attacks surprising: Shroff has consistently refused to let fellow doctors review her work or let them scrutinise her claims to have successfully treated more than 300 patients with a form of embryonic stem cell treatment devised by herself.

Shroff's clinic is part of a worrying trend around the globe - of clinics operating outside the medical establishment and offering stem cell therapy as a miracle cure. 'Clinics such as this are tapping into people's vulnerability. When you are drowning, you'll clutch at anything,' said stem cell expert Dr AK Bisoi of the All-India Institute of Medical Sciences, India's leading government hospital. '[Shroff] has been claiming she is doing this work, but we don't really know how she is doing it.' Bisoi said sophisticated equipment was necessary to administer injections into the spinal cord, as well as to harvest, develop and safely preserve stem cells. He said he had not seen any such equipment when he visited the clinic on its opening three years ago.

Such criticisms contrast vividly with the enthusiastic testimonies of Shroff's patients, however. Sonya Smith, 45, an Australian mother of three, who broke her back in a car accident two years ago, was told she would never walk again by her doctors in Brisbane. Then she heard reports of Shroff's apparent success in treating other paraplegics and came to Delhi. After 10 weeks of treatment, Smith said she had regained enough control over her legs to begin walking with callipers. She was also regaining control over her bladder and bowel movements.

Smith was unequivocal about the benefits of Shroff's treatment: 'I am walking, with callipers and a walking frame. Doctors have suggested that it was just a placebo effect. If that's true, give us all a placebo.'

As for Shroff, she is incensed by claims that her results are merely the results of the placebo effect. 'How dare scientists around the world refer to this as a placebo effect,' she said. 'They are rubbishing my work without seeing the patients.'

On the other hand, other doctors are suspicious because Shroff has never published her findings. They view her claim to have developed her own embryonic stem cell line as implausible and point out that there is no way of verifying her work, nor is there anyway of knowing whether she is actually treating patients with embryonic stem cells. Regulation of private medical clinics is lax in India and a draft law governing the use of embryonic stem cells has not yet been passed, a point stressed by Professor Sujata Mohanty, who is drawing up ethical guidelines.

'The problem is that until those guidelines become law, no action can be taken against her ... If she is doing such wonderful research, why doesn't she show us? She won't reveal her standard operating procedures. When we ask her, she says: "Speak to my lawyers."'

It was impossible to comment on the media reports of spectacular successes, Mohanty added, without being able to examine the patients before and after treatment. 'She is not the only one. There are other small clinics around Delhi taking advantage of this wave of excitement surrounding stem cell research. They are charging huge amounts of money to inject stem cells.'

This last point was also stressed by Dr Satish Totey, stem cell research director at Manipal Hospital, Bangalore. He said he was concerned that 'hopeless and desperate people' were being exploited.

Shroff dismissed her critics: 'As for peer review, what is that? Review by people who understand what you are doing. But no one understands what I am doing because I am the first. '

A brochure for her clinic summarises the treatment on her first 100 patients. 'Human embryonic stem cells transplantation brings "order" in a body system where the cells have lost their functioning ... When injected, there is a rapid and substantial improvement of mental and physical activities of the patients.'

As an example, Shroff pointed to Smith. 'Her spine was totally crushed,' said Shroff. 'She had no sensation beneath the level of the injury and was using catheters and diapers. Now she has sensation to her knees and is moving her toes gently.'

It is unlikely to satisfy her critics.