beta-Glucuronidase cleaves beta-glucuronides of drugs, steroids, as well as macromolecular compounds containing glucuronic acid bound with a beta-glycoside bond. Therefore, the study of induction of this enzyme by known microsomal enzyme inducers is of obvious interest. The effect of phenobarbital, spironolactone and pregnenolone-16 alpha-carbonitrle on the rat liver beta-glucuronidase was studied. These compounds augmented the activity of this enzyme, in the above increasing order. These results are discussed in view of the influence on pharmacokinetics of many drugs. Furthermore, they may lead to new therapeutic approaches for certain diseases.