Cisplatin was preincubated with equimolar GSH, Cys-Gly, or N-acetylcysteine in HBSS with 5 mM HEPES (pH 7.2) at 37°C for the times indicated to allow for the spontaneous formation of cisplatin conjugates. The toxicity of the mixture was assayed by treating LLC-PK1 cells for 3 h with 100 µM cisplatin preincubated with GSH (A), 100 µM cisplatin preincubated with Cys-Gly (B), or 100 µM cisplatin preincubated with NAC (C). The number of viable cells was determined at 72 h. Bars, values are the mean of three measurements ± S.D.