Acinar cells from guinea pig pancreas possess two distinct protein kinase activities. Cyclic GMP-dependent kinase elutes as a single peak on diethylaminoethyl (DEAE)- cellulose chromatography, is not inhibited by protein kinase inhibitor, and has a greater affinity for cyclic GMP (half-maximal activation at 20 nM) than for cyclic AMP (half-maximal activation at 100 nM). Cyclic AMP-dependent kinase elutes as two peaks on DEAE-cellulose chromatography, is inhibited by protein kinase inhibitor, and has a greater affinity for cyclic AMP (half-maximal activation at 20 nM) than for cyclic GMP (half-maximal activation at 7 micrometer). Binding of cyclic 3H-nucleotides to the enzyme preparation was rapid, specific, temperature-dependent, and reversible, and there was a close correlation between the ability of a particular cyclic nucleotide to inhibit binding of cyclic 3H-nucleotide and its ability of a particular cyclic nucleotide to inhibit binding of cyclic H-nucleotide and its ability to activate protein kinase. Binding of cyclic 3H--nucleotide could not be described as a simple bimolecular reaction and native cyclic nucleotides accelerated the dissociation of bound, labeled cyclic nucleotide. Vasoactive intestinal peptide or secretin, each of which increases cellular cyclic AMP, caused endogenous activation of protein kinase and inhibition of cyclic [3H]AMP binding but did not alter bindings of cyclic [3H]GMP or cyclic [3H]AMP.