We studied the influence of the ketamine maintenance dose on propofol infusion speed, blood pressure change and recovery time in anesthesia using propofol, ketamine and nitrous oxide. Anesthesia was maintained with ketamine 0.6 or 0.2 mg.kg-1.hr-1. The ketamine maintenance dose exerted no influence on propofol infusion speed, the occurrence of hypertension or hypotension. The recovery time correlated with the total amount of ketamine. From these results we conclude that 0.2 mg.kg-1.hr-1 is an appropriate maintenance dose of ketamine in anesthesia using propofol, ketamine and nitrous oxide.