Photopheresis (ECP) is a new therapy for oncological and autoimmune diseases consisting in the reinfusion of 3-9 x 10(9) leukocytes, taken from the patient by leukapheresis, and treated in an extracorporeal system with 8-methoxypsoralen and ultraviolet light A. Nine patients affected by T cell immunomediated diseases (2 scleroderma, 1 chronic GVHD, 1 polyarteritis, 1 rheumatoid arthritis and 4 heart transplant patients with numerous episodes of acute rejection) were treated with ECP. Photopheresis was performed on 2 consecutive days every 3-4 weeks. All patients affected by autoimmune diseases experienced an improvement during treatment with ECP. In 2 of the 4 patients with heart transplant, rejection was reversed by photopheresis. No major side effects were observed during the treatment. In conclusion ECP is a safe and well tolerated therapy. Although the number of patients is small, ECP seems to be an effective modality in many diseases.