The mechanism of human interleukin (IL)-1 beta-mediated cytolysis was studied in a human melanoma cell line, A375.6. Purified recombinant human IL-1 beta produced 50% cytocidal activity at 50 pg/ml. A variety of compounds were tested for their ability to interfere with A375.6 lysis. Compounds were added simultaneously with IL-1 beta (100 pg/ml), and tumor cytolysis was measured after 72 hr of culture by release of 125I from DNA of A375.6 cells labeled with [125I]-dUrd. A variety of anti-inflammatory/immunosuppressive agents (including auranofin, chloroquine, cyclosporin A, d-penicillamine) and several cyclooxygenase/lipoxygenase inhibitors (AA-861, BW755c, and indomethacin) lacked protective activity. Similarly, phospholipase inhibitors (mepacrine and 4-bromophenacyl bromide), putrescine, inhibitors of lysosomal activity (chloroquine and NH4Cl), calcium channel blockers (nifedipine and verapamil), calmodulin inhibitors (W-7 and calmidazolium), and inhibitors of ADP ribosylation (nicotinamide and 3-aminobenzamide) were inactive. In contrast, corticosteroids (dexamethasone, hydrocortisone, and paramethasone acetate), tilorone, and protein kinase C inhibitors (1-[5-isoquinolinyl-sulfonyl]-2-methylpiperazine and staurosporine) significantly inhibited IL-1 beta-mediated A375.6 cytolysis. These compounds also interfered with tumor necrosis factor-mediated lysis of A375.6, suggesting common mechanisms of tumor cytotoxicity by these monokines. This model may be useful for delineating intracellular biochemical events integral to IL-1 action.