Five commercial factor VIII (FVIII) concentrates and three prothrombin complex concentrates (PCC) were studied with reference to the qualitative evaluation of factors II, IX, fibronectin, α2-antiplasmin α2-AP), antithrombin III (AT-III) and subunits A and S of FXIII by crossed-immunoelectrophoresis (CIE) and von Willebrand factor antigen (vWF: Ag) by radio-CIE. This latter protein had a different pattern with the absence or a decrease of larger forms and the presence of a fast-moving precipitating peak, suggesting degradation of the vWF:Ag in FVIII concentrates. In contrast, the electrophoretic mobility of fibronectin, α2-AP and AT-III was normal. All PCC showed a more anodic mobility of factor IX. Α2-AP also exhibited a different electrophoretic pattern to that of normal plasma. Abnormality of AT-III was also found in heparin-binding studies. The techniques used in the purification procedures are probably the mechanism responsible for the partial denaturing of these proteins.