LLC-PK1 cells have been used as an in vitro model to study the nephrotoxicity of the antitumor drug cisplatin. A concentration-dependent cytotoxicity of cisplatin, measured as lactate dehydrogenase leakage and amount of protein remaining attached to the culture plate, was observed. At a cisplatin concentration of 0.4 mM cell viability was reduced to 21% after 72 hr. Ebselen, a seleno-organic compound capable of forming selenol intermediates through reaction with thiols, was found to protect LLC-PK1 cells against cisplatin-induced toxicity at low concentrations (5-15 microM). The ebselen-induced protection against cisplatin toxicity in this in vitro test system apparently correlates well with a similar protection previously observed in vivo in mice and rats.