Glucocorticoids are potent and diverse in their effects on mononuclear phagocytes, ranging from suppression to stimulation. To determine whether glucocorticoids affected functions mediated by monocyte beta-glucan receptors, human mononuclear cells (MNC) were incubated for 20 hr at 37 degrees with 20-2000 nM dexamethasone or hydrocortisone, and the monocytes were subsequently assayed for their ingestion of purified yeast glucan particles. Prior treatment with dexamethasone or hydrocortisone enhanced monocyte phagocytosis of glucan particles in a dose-dependent manner and both steroids effected a twofold increase at 200 nM. Monocytes from three different donors were assessed for secretion of beta-N-acetylglucosaminidase, and all were increased by exposure to 200 nM dexamethasone for 20 hr and subsequent stimulation with glucan particles for 2 hr; the average percentage net release was 16.2%. The enhancement in monocyte phagocytosis of glucan particles did not result by culture of MNC with beta-oestradiol, progesterone, testosterone or spironolactone, indicating a specificity for corticosteroids with glucocorticoid activity. The increases in phagocytic activity by monocytes that had been exposed during culture to either 200 nM dexamethasone or 200 nM hydrocortisone were both reduced by 40-50% by pretreatment of monocytes with the anti-idiotype (anti-Id) that recognizes beta-glucan receptors. Exposure of cells to 200 nM dexamethasone for 2 hr and washing before continued incubation for 18 hr in steroid-free media resulted in stimulation of monocyte beta-glucan receptors, whereas similar exposure without subsequent culture or with the addition of cycloheximide for the final 18 hr did not. Thus, glucocorticoids enhance monocyte functions mediated by beta-glucan receptors, and this stimulation is dependent on proteins that are newly synthesized during culture.