The beta-glucan receptor, found on monocytes and neutrophils, binds glucose polymers derived from fungi. Ligands for the receptor have various immunomodulatory effects, including increased microbicidal killing activity. We have investigated the effect of beta-glucans on the production of interleukin-1 (IL-1) and its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1Ra). Particulate beta- glucan induced IL-1Ra production from human peripheral blood mononuclear cells (PBMC) but did not stimulate IL-1 beta synthesis or gene expression in these same cells. Monomeric (soluble) beta-glucan did not induce IL-1Ra production. However, when preincubated with PBMC, monomeric beta-glucan significantly (P <.01) reduced particulate beta- glucan induction of IL-1Ra by 40%, suggesting that crosslinking of beta- glucan receptors is required for induction of IL-1Ra. In support of this, monomeric beta-glucan immobilized on plastic surfaces stimulated IL-1Ra production. Vitamin D3, which increases the functional capacity of beta-glucan receptors, increased IL-1Ra production induced by particulate beta-glucan, whereas dexamethasone suppressed IL-1Ra synthesis. Because of their differential effects on cytokine production, beta-glucans may be used to therapeutic advantage in the diseases in which IL-1 is implicated.