We studied the effect of combined treatment with cisplatin, glucosaminylmuramyl dipeptide, and TNF-alpha on viability of MCF-7, U-937, B16, and L-929 tumor cells, Ehrlich ascites carcinoma cells, and normal cells (human peripheral blood lymphocytes, peritoneal macrophages, and mouse bone marrow cells). Glucosaminylmuramyl dipeptide was nontoxic for normal and tumor cells, but promoted death of tumor cells after administration in combination with cisplatin and/or TNF-alpha. At the same time, glucosaminylmuramyl dipeptide did not modulate the cytotoxic effect of individual or combined treatment with cisplatin and TNF-alpha on normal cells. Administration of glucosaminylmuramyl dipeptide to cultured MCF-7 cells 20 h before the study increased the potentiating effect of muramyl peptide.