Factor IX falloff studies in three rhesus macaques 84269, RQ 1234, and RQ 1305. Each animal was studied on four occasions by injecting 25 units Mononine/kg body weight followed by immunoassay for human factor IX at the indicated time points. Falloff studies were performed by single injection of factor IX at T = 0, 80 days, and 162 days; three daily injections of factor IX were performed 10 days before a fourth falloff study at T = 388 days to maximize the chance that any immune response might be boosted.