extracorporeal photopheresis (EK-struh-kor-POR-ee-ul FOH-toh-feh-REE-sis)
A procedure in which blood is removed from the body and treated with ultraviolet light and drugs that become active when exposed to light. The blood is then returned to the body. It is being studied in the treatment of some blood and bone marrow diseases and graft-vs-host disease (GVHD). Also called photopheresis.