We have determined the effect of glutathione (GSH) depletion on the cytotoxicity of three nitrogen mustards, six platinum complexes, and mitomycin C in a human ovarian carcinoma cell line. GSH levels in COLO 316 cells were depleted by exposure of cell monolayers to 0.5 mM D,L-buthionine-S,R-sulfoximine. GSH depletion significantly potentiated the cytotoxicity of L-phenylalanine mustard, chlorambucil, and mechlorethamine as determined by clonogenic assay on plastic plates. The dose modification factors were 2.6, 2.6, and 1.9, respectively. The same level of GSH depletion had a minimal effect on the cytotoxicity of cis-diamminedichloroplatinum(II) (cis-DDP), carboplatin, dichloro(ethylenediamine)platinum(II), 1,2-diaminocyclohexylplatinum(II) malonate, and iproplatin. The dose modification factors of GSH depletion for these drugs were 1.4 or less. trans-Diamminedichloroplatinum(II) was, however, markedly potentiated by GSH depletion with a dose modification factor of 2.7. Mitomycin C was minimally potentiated by GSH depletion. We have also generated cis-DDP-resistant cells from COLO 316 and 2008 human ovarian carcinoma cells by in vitro selection with cis-DDP. These cis-DDP-resistant cells had identical levels of GSH as the parental cells. GSH depletion sensitized these cells only to the same degree as the parental cells and did not reverse the resistant phenotype. Our results indicate that intracellular GSH levels are not an important determinant of the cytotoxicity of cis-platinum(II) or cis-platinum(IV) complexes in COLO 316 and 2008 cells. In addition, altered GSH metabolism does not appear to be a component of the cis-DDP-resistant phenotype in these cells.