Protein kinase C in rat cerebral microvessels was characterized. By hydroxyapatite column chromatography, protein kinase C in the soluble fraction was resolved into two major peaks corresponding to type II and III enzymes, in the proportion of 57% and 38%, respectively. Since each subtype is considered to have a distinct role, the high proportion of type II enzyme found in this study suggests that this type may be involved in specific functions of the cerebral microvessels.