The biosynthesis of poly(A) containing RNA in the cultured rat pineal was monitored during the isoproterenol-induced increase in N-acetyltransferase activity in the presence of various inhibitors of RNA synthesis. The induction of N-acetyltransferase in the pineal gland by the β-agonist isoproterenol was found to be inhibited by actinomycin D and α-amanitin, but relatively insensitive to cordycepin. The concentration of actinomycin D which inhibits the induction process 50 per cent is on the order of 5 μg/ml, whereas only 0.1 μg/ml is needed to inhibit poly(A)-containing RNA synthesis by 50 per cent. Cordycepin, which inhibits the addition of poly(A) into newly synthesized messenger RNA, inhibited poly(A)-containing RNA synthesis by 85 per cent but inhibited the induction of N-acetyltransferase by isoproterenol only 15 per cent. The mushroom toxin a-amanitin, which should preferentially inhibit messenger type RNA synthesis, reduced poly(A)-containing RNA synthesis 50 per cent at 10 μg/ml of toxin, and inhibited enzyme induction 50 per cent at 40 μg/ml. While these results support the participation of an RNA species in the apparent induction of N-acetyltransferase in the pineal gland, they suggest that the induction stimulus may not be exerting its effect by simply causing an increase in the synthesis of messenger RNA containing a poly(A) terminus.