Helothane hepatitis is a rare but sometimes fatal complication of halothane anaesthesia. Examination of case reports has pointed to a number of risk factors. Studies in animals and humans in the laboratory have provided evidence of a complex multifactorial basis for halothane hepatotoxicity, with the following factors playing a part: genetic predisposition; metabolism of halothane; repeated halothane anaesthetics; female sex; age of patient; intrahepatic hypoxia; and enzyme induction. Immunologic changes can be detected in a high percentage of cases of halothane hepatitis; however, studies establishing a cause-effect relationship are not available to determine if these changes cause, or result from, hepatic damage.