The present study has been to test the effect of hydrocortisone (HC) on the mitotic incidence in adrenocortical cells of organ-cultured rat adrenal explants during a 24-hour incubation with or without angiotensin II (ANG). It was shown that HC significantly decreased the mean mitotic activity rate (MMAR) of adrenocortical cells in organ culture. That decrease concerned all the three cortical zone vs respective controls. In turn, ANG markedly increased the MMAR of the zona glomerulosa cells, when compared to the values recorded in controls, while there were no changes of the MMAR of the zona glomerulosa in the adrenal explants incubated with joint exposure to HC and ANG. The obtained results indicate that HC exhibits an inhibitory effect on the adrenocortical cell proliferation, which may suggest that arachidonic acid metabolites play an important role in the process of adrenocortical hyperplasia, their participation in the ANG-induced zona glomerulosa cell proliferation being strongly assumed.