Photopheresis (ECP) is a new type of photochemotherapy, used for the treatment of oncological and autoimmune diseases. Lymphocytes are drawn from the patients by leukapheresis, treated with 8-methoxypsoralen (8-MOP) and ultraviolet light A (UVA) in an extracorporeal system and then reinfused. Skin exposure to 8-MOP and UVA (PUVA) has been shown to relieve cutaneous symptoms of graft-versus-host disease (GVHD) in bone marrow transplant (BMT) recipients. ECP, which is similar in some ways to PUVA, has been used in this study to treat four paediatric patients who developed chronic GVHD following BMT and in whom GVHD had failed to respond to conventional immunosuppressive therapy. Following ECP, skin lesions cleared almost completely and pulmonary function tests improved in two of three patients with cutaneous and lung involvement. Serum bilirubin and transaminases gradually normalized, and gammaGT decreased considerably in the remaining patient who had a severe cholestatic hepatopathy. The Karnofsky performance score increased to 90% in the three patients with positive responses to ECP and remained unchanged (40%) in the patient who did not respond. Immunosuppressive therapy was reduced in three patients and eventually discontinued in two. No significant side-effects were observed during the treatment. Our results suggest that ECP is a non-aggressive treatment that may benefit patients with chronic GVHD who do not respond to standard immunosuppressive therapy.