[(3)H]N(6)-(Ethyl 2-diazomalonyl)-adenosine 3':5'-cyclic monophosphate is incorporated into intact ghosts from human erythrocytes on photolysis at 253.7 nm. Incorporation is blocked in the presence of adenosine 3':5'-cyclic monophosphate (cyclic AMP) and does not occur in the absence of irradiation. Sodium dodecyl sulfate disc gel electrophoresis of solubilized ghosts shows that one protein is labeled. The position of this protein on the gel corresponds exactly to that previously found. [J. Biol. Chem. 247, 8145 (1972)] for the endogeneous protein substrate of the endogenous, cyclic AMP-dependent, protein kinase.