Thursday, 22 June, 2000, 00:06 GMT 01:06 UK
Powerful drugs are given to the patient Bone marrow transplants are already used to help cancer patients - but sufferers of serious immune system disease could also benefit.
However, the risks involved with the treatment mean that only the most severely affected are likely to be offered it in future.
Conditions such as multiple sclerosis and rheumatoid arthritis are believed to be caused by the body's own immune system turning on its tissues.
In severe cases of rheumatoid arthritis, not only the joints, but also the internal organs are affected, even endangering the life of the patient.
Existing treatments work by using powerful drugs to suppress the body's immune system.
The bone marrow treatment goes one stage further.
Immature cells, called stem cells, are taken from the patient's bone marrow, and then even more powerful doses of drugs used to completely "kill off" key immune system cells.
Once this has been completed, the stem cells are put back in and the immune system slowly regenerates - hopefully without turning on its own body.
Professor Alan Tyndall, from the Felix-Platter Spital in Basle, Switzerland, reported the results of a major trial into the technique involving 275 patients with scleroderma at a European rheumatology conference held in Nice.
Scleroderma is a rare autoimmune disease affecting the skin and major organs.
Two-thirds of the patients - who all suffered severely from the condition - benefited from the treatment.
Prof Tyndall urged caution about the future prospects of the treatment.
He said: "Patients with progressive multiple sclerosis or untreatable scleroderma feel desperate.
"Despite its scientific merit, this new form of bone marrow transplantation can be dangerous."
The Arthritis Research Campaign is funding similar research into stem cell transplantation for rheumatoid arthritis in Leeds.
Its medical advisor, Dr Madelaine Devey, said: "It's an exciting idea, but not without hazards.
"You're getting rid of the whole immune system, which leaves patients very vulnerable to infection.
"So it would only be used as a treatment for the most seriously ill patients."