A study of the involvement of glutathione (GSH) in cellular resistance to cisplatin was performed using methylmercury-resistant sublines (PC12/TM series) of the PC12 line of rat pheochromocytoma cells. The seven clonal sublines of PC12 cells (PC12/TM, PC12/TM2, PC12/TM5, PC12/TM11, PC12/TM15, PC12/TM23, PC12/TM26) used in the study had intracellular levels of GSH that ranged from 8.7-39.9 nmol/mg protein. The intracellular level of GSH was significantly correlated (p < 0.01, r = 0.87) with the sensitivity to cisplatin of PC12 cells and the seven sublines. Among the seven sublines, PC12/TM cells contained the highest concentration of GSH and were the most resistant to cisplatin. Treatment of PC12/TM cells with L-buthionine-SR-sulfoximine, which reduced the level of GSH to that in the parental PC12 cells, significantly reduced the resistance of the cells to cisplatin. The amount of platinum accumulated by resistant PC12/TM cells after treatment with cisplatin was higher than that by sensitive PC12 cells. These results suggest that the intracellular level of GSH might be directly involved in the resistance to cisplatin of these cell lines. However, a high intracellular concentration of GSH does not appear to contribute to a decrease in the accumulation of cisplatin in these cells.