We compared the protein kinase C isoenzyme patterns of crude extracts of rabbit brain, cerebellum, spleen, thymus and human and pig granulocytes. The isoenzymes were fractionated by hydroxyapatite chromatography and the protein kinase C activity was determined with a synthetic oligopeptide substrate. In the extracts of several tissues we also observed an enzyme fraction which was activated by phosphatidylserine + diacylglycerol but inhibited by Ca z÷.Protein kinase C; Synthetic ofigopeptide substrate; Isoenzyme; Ca2+-inhibited enzyme fraction