The authors have compared two groups of 31 patients each, undergone an anaesthesia with propofol-O2/N2O (group I) and propofol-O2/air (group II). The average anaesthetic dosage and the neuromuscular recovery time have been valued, keeping constant the dose of analgesic. The average consumption of propofol (except the inductive dose of 2 mg/kg) was 7.41 +/- 1.71 mg/kg/h in group I, and 7.47 +/- 1.76 in group II (p = 0.88; not significant) and the neuromuscular recovery time 56.12 +/- 34.55 m' and 49.48 +/- 40.50 m' respectively (p = 0.53; not significant). The cardiocirculatory parameters have been compared at the time of induction, surgical incision and for all the operation time, reporting every undesired effect. The awakening has been monitored until 15 m' from the interruption of propofol infusion. The data obtained don't permit to observe significant differences with regard to analgesia, neuromuscular block and awakening time. Therefore the authors put the question of the real necessity to use nitrous oxide, when it has utilized an efficient intravenous anaesthetic as the propofol has proved to be.