The acute cytotoxicities of chloroquine sulfate, propranolol, ascorbic acid, acetylsalicylic acid and acrylamide on cultured adult rat hepatocytes were evaluated by the use of LDH leakage and NR uptake test. On the basis of IC_(50) values, the rank order of cytotoxicities of these drugs in both tests was chloroquine sulfate > propranolol > acetylsalicylic acid > ascorbic acid. The IC_(50) of LDH test was very similar to that of NR uptake test. Thus, we concluded that both tests are reliable and sensitive methods in detecting toxicity in adult cultured rat hepatocytes.