documented in which such multiple drug therapy has created problems. For example, a patient receiving barbiturates requires an increased dose of an anticoagulant to obtain the desired reduced clotting of blood. The reason for this effect is thought to stem from the barbiturateproduced stimulation of the metabolism of the anticoagulant. However, when the barbiturate treatment is discontinued, the same dose of anticoagulant becomes excessive and severe bleeding may result. Consequently, a reduction in dosage of the anticoagulant is necessary when barbiturate treatment is stopped. The question then arises whether a drug which stimulates the metabolism of other drugs can be used to eliminate from the body unwanted substances, either endogenous, such as steroid hormones, or foreign, such as pesticides. Some preliminary evidence which suggests that this may be possible has been obtained and will be presented in this article. The study of the increase in enzyme activity (induction) by drugs had its beginning about 15 years ago, with the discovery by the Millers and their students at the University of Wisconsin Medical School, that the administration of various foreign substances into animals increased the activity of certain liver enzymes. Because of the initial observation that these enzymes are primarily involved in the metabolism of drugs and other foreign fat-soluble substances, these enzymes have been called drug-metabolizing enzymes. These findings aroused the curiosity of investigators interested in the study of drug action, notably the pharmacologists. However, more recently, the realization that these enzymes may have a more general function, namely, the ability to metabolize endogenous substances as well, prompted scientists from other biological disciplines, such as physiology, biochemistry, and medicine, to be drawn into this sphere of research. This explosion of interest in the field of d ug-metabolizing enzymes should lead to rapid progress both along basic and applied lines.