We have previously reported that interleukin-1 (IL-1 ) sensitized cisplatin cytotoxicity against human ovarian NIH:OVCAR-3 tumor cells. We have further examined inter-actions of IL-1 with cisplatin in these ovarian cells. Treatment of cells with either IL-1 or CDDP or combinations resulted in a significant accumulation of cells in G1 phase and a concomitant decrease in the S phase of the cell cycle. IL-1 and CDDP treatment induced p53 protein in NIH:OVCAR-3 tumor cells. CDDP and IL-1 treatment decreased the steady-state expression of c-myc RNA and induced significant degradation of the genomic DNA into internucleosomal sized DNA fragments which was further increased in the presence of both agents in these cells. Taken together, these studies suggest that IL-1 may kill ovarian NIH:OVCAR-3 tumor cells by inducing a blockade at G1/S of the cell cycle, down-regulating c-myc gene and inducing p53-dependent apoptosis. The synergistic interactions of IL-1 with CDDP may involve the enhancement of p53-dependent apoptosis.