AbstractDexamethasone inhibited the basal and EGF‐stimulated DNA synthesis of adult rat hepatocytes in primary culture. The inhibition was glucocorticoid‐specific: It was shown by dexamethasone and hydrocortisone, but not by progesterone, testosterone, or estradiol; and was counteracted by the glucocorticoid antagonist RU‐38486 in a concentration‐dependent manner. Dexamethasone acted by decreasing the rate of entry into S‐phase (kG1/S), while cell cycle parameters were unaffected. The steroid was able to decrease the kG1/Sseveralfold even when added more than 20 hr after EGF, half‐maximal effect occurring 11 hr after the addition of dexamethasone. Densily populated areas were much more sensitive to the inhibition by dexamethasone than sparsely populated areas within the same culture dish: A moderate (10 nM) concentration of dexamethasone nearly abolished the DNA synthesis in densily populated areas of hepatocyte cultures with only marginal effect on sparsely popu