Glucocorticoids have profound and complex effects on the human immune response. However, the precise mechanisms of the corticosteroid-induced immunoregulation in man have not been precisely defined. Intracytoplasmic corticosteroid-specific receptors appear to be an important common pathway for steroid-induced changes, but variations of receptor parameters do not account for the multifaceted effects on the immune system. Human circulating mononuclear cells redistribute out of the intravascular compartment following treatment with corticosteroids. Although certain components at this redistribution phenomenon have been well-characterized, the importance of this compartmental cellular shift with respect to the mechanisms of corticosteroid-induced immunoregulation are less well-defined. Recent observations that activated lymphocytes may be sensitive to the lytic effects of glucocorticoids suggest that under certain situations the elimination of selected subsets of cells may be a relevant mechanism of corticosteroid-mediated immunoregulation in man. Corticosteroid-mediated effects on monocyte function may be an important mechanism of drug-induced immunoregulation in monocyte-dependent responses. In some experimental conditions, corticosteroids inhibit Interleukin 1 production by monocytes. The immunoregulatory effects of corticosteroids on lymphocyte immune responses are complex. In vitro corticosteroids appear to selectively affect early immunoregulatory events as opposed to altering an established response. Multiple sites of steroid-induced modulations of human B cell responses have been defined.