A 42 year-old woman develops steroid refractory graft-versus-host disease (GVHD) after second allogeneic stem cell transplantation for acute myelogenous leukemia with severe GVHD of her skin with blisters, severe GVHD of her gut with watery and bloody diarrhea and GVHD of her liver with cholestasis. In a further attempt to control GVHD extracorporeal photochemotherapy is administered. The treatment exposures peripheral mononuclear cells to photoactivated psoralen before they subsequently are given back to the patient. This approach apparently offers selective immune tolerance.