In an attempt to identify compounds with antihepatotoxic activity, carbon tetrachloride-induced cytotoxicity in primary cultured rat hepatocytes has been adopted as a screening system. Using this screening system, an antihepatotoxic compound from the aerial parts of Epimedium koreanum has been isolated. This compound, icariin, is a flavonol glycoside. Its antihepatotoxic activity was first evaluated by measuring the release of glutamic pyruvic transaminase and sorbitol dehydrogenase from CCl4-intoxicated rat hepatocytes into the culture medium. Icariin significantly reduced the level of glutamic pyruvic transaminase and sorbitol dehydrogenase released resulting in a 76% protection from toxicity at concentration ranges from 1 µM to 20 µM. The antihepatotoxic activity of icariin was also estimated by the determination of total cytochrome P-450 content and glutathione-S-transferase activity in the CCl4-intoxicated hepatocytes.