We have investigated the possible hepatic microsomal enzyme induction effect of enflurane, administered by inhalation in anaesthetic doses for periods of 1 h a day. In 15 experimental groups, differing from one another in anaesthetics concentration (1, 2 and 3% enflurane) and in the number of days of treatment (3, 7, 10, 14, 21 and 24) we found (1) no alteration either in the ratio of liver to body weight or in the microsomal protein content; (2) no modifications in aniline hydroxylase activity; (3) a decrease in the aminopyrine demethylase activity after a number of exposures, varying with the dose.