A patient with several episodes of jaundice associated with sulfamethoxazole therapy is described. In contrast to the histologic picture of hepatocellular necrosis with or without cholestasis that is generally associated with sulfonamide hepatotoxicity, in the present case a relatively pure cholestatic pattern was found. Associated clinical features, as well as the response to drug challenge, were compatible with a hypersensitivity mechanism. The patient's lymphocytes did not undergo in vitro blast transformation upon stimulation with sulfamethoxazole or sulfamethoxazole-containing plasmas.