Factor VIII procoagulant (VIII:C) activity, factor VIII coagulant antigen (VIII:CAg), von Willebrand ristocetin cofactor (VIIIR:RC) activity, factor VIII-related antigen (VIIIR:Ag), and plasma fibronectin (CIg; cold-insoluble globulin) were measured in the heparin precipitable fraction (HPF) and heparin supernatant fraction (HS) of normal human plasma. Following heparin induced precipitation, most measurable VIII:C activity (77% +/- 24%) was recovered in the HS. Although there was little VIII:C activity (less than 1%) in the HPF, 20% +/- 6.5% VIII:CAg was present as well as CIg (81% +/- 5.6%). VIIIR:RC activity (72% +/- 12%), and VIIIR:Ag (34 +/- 5.2%). As assessed by Na dodecyl SO4 glyoxyl agarose electrophoresis, the multimeric forms of plasma VIIIR:Ag could be resolved into a series of bands. Larger multimers tended to precipitate with the HPF whereas the smaller multimers tended to remain supernatant. Plasma from a subject with congenital afibrinogenemia was also studied. Although the afibrinogenemic HPF contained CIg, neither VIIIR:RC activity nor VIIIR:Ag was precipitated. However, both were present in the HPF from afibrinogenemic plasma to which fibrinogen had been added, suggesting that they are incorporated in this precipitate because of an affinity for fibrinogen. The ability of heparin to induce precipitation of CIg while leaving most VIII:C activity in the supernatant plasma may be useful in the preparation of procoagulant-rich plasma subfractions, since VIII:C can subsequently be recovered in good yield by cryoprecipitation.