The effect of dexamethasone on the in vitro release of IL-1 and IL-3-LA by human unstimulated mononuclear cells was studied. The drug elicited a dose-dependent effect on the production of both interleukins. In addition, a time course effect of dexamethasone on IL-3-LA was demonstrated. It appeared after 5 min of incubation, reached a maximal level after 15 min, and remained at that level after 24 h. The drug also caused a dose-dependent inhibitory effect on the ability of human mononuclear cells to incorporate [3H] uridine. The inhibitory effect of dexamethasone on these interleukins may serve as a partial explanation of the susceptibility to infection in patients treated with corticosteroids. IL-3-LA / dexamethasone / mononuclear cells.