Extracorporeal photochemotherapy is a recently developed immunomodulator treatment against heart and lung graft rejection. The recipient's mononuclear cells are screened and irradiated with UV-A in the presence of 8-methoxy-psoralene (8-MOP), then reinjected. We treated 4 patients who had begun to reject their heart and/or lung grafts, with this technique, using one session per week for 4 weeks, followed by one session every 2 weeks for 2 months, then one session per month. In all cases, extracorporeal photochemotherapy appeared to improve the clinical and biological status of these patients. Episodes of rejection which could not be reversed with immunosuppressor treatment alone were controlled.