The appearance of an acquired inhibitor to factor VIII clotting activity (F VIII:C) in a non-haemophiliac is an uncommon phenomenon; but, when it occurs, represents a difficult therapeutic problem. Cyclophosphamide has been the most frequently used form of therapy while corticosteroids, when used alone, have been felt to be ineffective. During the past 25 years, 18 of these patients have been evaluated in Pittsburgh. Their mean age was 63.7 years. Nine were female and nine male. Sixteen of the 18 received corticosteroids as their primary form of therapy. Eleven of the 16 (69%) showed clinical and laboratory improvement. Seven of the 11 had a complete response and the remaining four a partial response. Five patients demonstrated no improvement with corticoid therapy. The time to response varied from 4 to 41 d (mean 15.8). It was concluded that corticosteroids when used alone provide therapeutic results comparable to immunosuppressive therapy in the treatment of acquired inhibitors to F VIII:C and therefore represent a therapeutic alternative to immunosuppressive agents.