The isolation of human plasma prekallikrein.

1. The isolation of human plasma prekallikrein was achieved by fractionating human plasma on diethylaminoethyl cellulose (DEAE) in the presence of heparin.2. Heparin was shown to inhibit the activation of prekallikrein during the isolation procedure.3. The isolated prekallikrein fraction had some kallikrein activity which could be inhibited by diisopropylfluorophosphate (DFP) without affecting the ability of prekallikrein to be activated.4. The prekallikrein obtained was functionally pure in that it had no kallikrein inhibiting or activating activity. It was not physico-chemically pure, the major contaminant being the immunoglobulin IgG.