At baseline, each subject received a physical examination, was questioned as to medical history, and gave blood samples for immunologic and other studies. Each subject returned at a specified interval for a repeat of studies specified in the protocol. Blood studies included complete blood cell count, characterization of immunologic cells such as T- and B-lymphocytes and natural killer-cells. Plasma and Buffy coat cell suspensions were stored frozen. Alanine aminotransferase levels were determined. Serologic tests were performed for hepatitis, Epstein-Barr virus, and cytomegalovirus. Markers of immune status, including immune globulin levels were measured. The study ended in November, 1997.