Two types of complementary DNA clones for rat brain protein kinase C were isolated. These clones encode 671 and 673 amino acid sequences, which differ from each other only in the carboxyl-terminal regions of approx. 50 amino acid residues. This difference seems to result from alternative splicing. Elucidation of the sequences of these cDNA clones as well as some peptides from the purified rat brain enzyme suggests the existence of an additional species of protein kinase C in this tissue. It is attractive to imagine that the heterogeneity of protein kinase C may reflect diverse pathways of signal transduction into the cell.