Two cyclic AMP analogues, l-chloro cyclic AMP and 8-(4 chlorophenyltbio) cyclic AMP, were found to increase the incorporation of rHJoleate into cholereryl ester in cultured hamster hapatocytes (30-40%), while incorporation into triacylglycerol was unaffected. An increase of a similar magnitude was observed in the presence of glucagon and the phosphodiesterase inhibitor, theophylline. The cyclic AMP analogues also stimulated the activity of neutral cholesteryl ester hydrolase in the cells, and this effect was mimicked by glucagon and theophylline. These results show that cyclic AMP can affect the cholesteryl ester cycle in hamster hepatocytes, and support the idea that the enzymes involved may be co-ordinately regulated.