The cellular mechanisms associated with the replicative response of hepatocytes to growth factor simulation is incompletely understood. Murine hepatocyte DNA synthesis is altered by cyclic AMP, suggesting that protein kinase A is involved in the cellular mechanisms associated with liver growth. The purpose of this study was to evaluate the role of protein kinase A in human hepatocyte DNA synthesis. human hepatocytes were isolated and maintained in primary culture on rat tail collagen. DNA synthesis was evaluated by determining [3H] thymidine incorporation. Human hepatocytes between 24 and 96 hr following harvest increased DNA synthesis in response to epidermal growth factor but not in response to glucagon, a stimulant of adenyl cyclase, or dibutyryl cyclic AMP. Mitogen-stimulated DNA synthesis was decreased by dibutyryl cyclic AMP. Cyclic AMP isomers that block or stimulate the effect of cyclic AMP on protein kinase A did not significantly alter resting or mitogens-stimulated human hepatocyte DNA synthesis. The results suggest that increased protein kinase A activity does not produce human hepatocyte replicative DNA synthesis.