1. Drug metabolism was assessed by the disappearance rate of antipyrine as measured in saliva. Results were expressed in terms of both clearance and half life. 2. Basal measurements of antipyrine disappearance rate were performed in seven non-smokers and six smokers. After administration of glutethimide 250 mg daily for 7 days a second measurement of antipyrine disappearance rate was made. 3. Glutethimide enhanced antipyrine metabolism in both smokers and non-smokers. The degree of change in both groups was similar. 4. A similar study was carried out with a smaller dose (125 mg) of glutethimide. There was no significant difference between smokers and non-smokers.5. The data are consistent with smoking and chronic drug ingestion having additive effects on enhancement of hepatic drug metabolism.