AbstractTo determine if heat‐treated factor IX complex concentrate is as effective as nonheated factor IX complex concentrate for treatment of subjects with hemophilia A and antifactor VIII antibodies (inhibitor patients), we have retrospectively reviewed consecutive home treatment records of ten inhibitor patients who had been receiving nonheat‐treated factor IX complex concentrate (NHT‐Konyne) and subsequently converted to heat‐treated factor complex concentrate (Konyne‐HT) when it was licensed in late 1984. Overall, 162 of 284 (57%) separate bleeding episodes treated with NHT‐Konyne and 53 of 80 (66.3%) separate bleeding episodes treated with Konyne‐HT required only one treatment course of ∼60‐75 U/kg. The distribution of bleeding sites and the absolute factor IX unitage required per treatment episode were similar for both preparations. These data suggest that the percentage of hemophilic inhibitor patients responding to factor IX complex concentrate remains at least 50%, as was reported several years ago in a controlled study, and that inhibitor bypass activity has not altered