Hydrocortisone sodium succinate (HC) inhibited "in vitro" neutrophil-mediated antibody-dependent cellular cytotoxicity (ADCC). The drug effect was dose-dependent and completely reversible. The killing defect was partially overcome by increasing the density of the antibody on the target cells. However, HC added after the binding between effector and target cells was still able to inhibit in a similar dose-dependent way the cytotoxic activity. Our results suggest that HC interferes in a later step, after the effector/target interaction. Methyl-prednisolone and dexamethasone as well as HC were found to inhibit in a dose-dependent manner the neutrophil-mediated ADCC, whereas testosterone did not have any effect.