The effect of advanced age on drug disposition and response is the subject of an increasing number of research studies. Cigarette smoking and other environmental factors have been shown to influence the metabolism of some drugs. Studies of the effect of age on the pharmacokinetics of antipyrine, indocyanine green and propranolol indicate that the association of increased drug metabolism and smoking occurs predominantly in the young and that apparent liver blood flow declines with age regardless of smoking habits. This age related effect of smoking on drug metabolism may reflect a reduced capacity for hepatic enzyme induction in the elderly. The relative importance of age related alterations in the intrinsic drug metabolising ability of the liver and in liver blood flow depend on the pharmacokinetic characteristics of the drug being investigated.