The propofol requirements for the induction and maintenance of anaesthesia were compared in groups of younger and older patients. Side effects, influence on the cardiovascular system and recovery times were compared between 20 unpremedicated ASA I-III, 25-40-yr-old patients and 20 65-80-yr-old patients all scheduled to undergo elective surgery. After induction with propofol, anaesthesia was maintained with a continuous infusion of the drug. Vecuronium and fentanyl were administered as required. In the young group propofol 2.2 mg kg-1 and in the elderly 1.7 mg kg-1 were needed for induction (P less than 0.05). The maintenance doses were 10.0 mg kg-1 h-1 and 8.6 mg kg-1 h-1, respectively (P less than 0.01). Side effects were more pronounced in the younger patients. Influences on the cardiovascular system were definite, but mild. The younger patients awoke sooner: 7.8 v. 14.3 min (P less than 0.01) after the discontinuation of the infusion of propofol.