Protein synthesis in the cultured rat pineal gland was monitored during the course of N-acetyltransferase induction by (l-isoproterenol or dibutyryl cyclic AMP. The incorporation of labeled amino acids into gland protein was essentially linear over a 6-h experimental period. Examination of the newly synthesized proteins by polyacrylamide gel electrophoresis and autoradiography did not reveal the appearance nor the disappearance of any specific protein(s) caused by (l-isoproterenol or (l)-propranolol. The lack of stimulation of synthesis of any specific protein was further demonstrated by constant ratio of incorporation in double-label experiments. Either 2μm (l)-isoproterenol or 1 mm dibutyryl cyclic AMP stimulated protein synthesis 20-40%. This increase was not due to an enhanced uptake of precursor radiolabeled amino acids by the glands when incubated with the β-agonist or cyclic AMP derivative. The stimulation of protein synthesis caused by (l)-isoproterenol was abolished by the β-antagonist (l)-propranolol. These results suggest that β-agonists may increase pineal gland protein synthesis through their relevant receptor and the generation of cyclic AMP. This increase in synthesis appears to be general and no selective elevation increase in any one band was observed.