The synthesis of melatonin in Xenopus retinas, chick and quail retinal cell cultures, and Y79 human retinoblastoma cells is stimulated by cAMP through a protein synthesis-dependent mechanism. In Y79 retinoblastoma cells, combined treatment with the RNA synthesis inhibitor camptothecin and agents that elevate cAMP, such as forskolin, causes a synergistic elevation of melatonin. Using two-dimensional gel analysis we have identified a 30 kDa cytosolic protein (p30) whose radiolabeling was consistently increased in parallel with increases in arylalkylamine N- acetyltransferase activity and melatonin production that were induced by forskolin and/or camptothecin. Pulse-chase experiments suggest that the elevation in radiolabeling of p30 is due to increased synthesis. Three candidate proteins found in the mammalian pineal, protein 14–3–3, malate dehydrogenase, and recoverin, do not comigrate with p30.