We examined 35 patients with hemophilia to determine if there was an association between impaired cell-mediated immunity and the amount of factor concentrate use. There was a significant negative relationship between the logarithm of the helper-suppressor ratio and the logarithm of concentrate use determined over the previous one year, five years, and total lifetime. Similarly, the presence of splenomegaly was significantly associated with the logarithm of concentrate use for each time interval. Hypergammaglobulinemia, anergy, and lymphadenopathy were present in a high proportion of patients. Repeated study of 30 of these patients at eight to 14 months showed no significant changes in their T-cell subsets. At follow-up, 16 patients had lymphadenopathy with or without splenomegaly and four had splenomegaly alone. No significant associations between concentrate use during the study period and changes in T-cell subsets or clinical condition were found.