A large pseudotumor was removed from a hemophiliac patient, necessitating the use of long-term, high-dose therapy with factor VIII concentrate. The patient's activated partial thromboplastin time rarely normalized in spite of high factor VIII assay levels. In addition, other routine tests of coagulation became abnormal. This was attributed to large quantities of either fibrinogen or other inhibitors, or both, in the infused factor VIII concentrates. It is postulated that if fibrinogen in great excess is the sole cause of these abnormalities it causes them by not being totally converted to fibrin, the excess interfering with fibrin polymerization.