The influence of anesthesia on plasma cortisol has most often been studied in connection with routine operations. To investigate the specific effects of modern inhalation anesthetics more accurately, we examined the specific effects of four inhalation anesthetics on human plasma cortisol during volunteer studies on the influence of anesthetics on the electroencephalogramm. METHODS. A group of 17 (10 m, 7 f) young healthy volunteers who had not received any premedication and were not intubated were studied after informed consent had been obtained. In the first series of experiments the concentration of halothane, enflurane, isoflurane or N2O was increased to MAC (minimal alveolar concentration) 0.5 for a 15-min steady-state period. Blood samples were taken 5 min prior to induction (I), 35 min after induction, on steady-state MAC 0.5 (II), and 15 (III) and 35 (IV) min after the end of anesthesia. In a second series, with 5 subjects, the concentration of halothane, enflurane or isoflurane was first increased to a steady state of MAC 1.0. After reduction to MAC 0.5 steady-state, anesthesia was supplemented with 53% N2O to give a steady state of MAC 1.0 again. Blood samples were taken 5 min prior to induction (I), after the attainment of steady-state MAC 1.0 (II), 35 min later at MAC 0.5 (III), 40 min later at MAC 1.0 with volatile anesthetic/N2O (IV), and 15 (V) and 35 (VI) min after the end of anesthesia. RESULTS. MAC 0.5 N2O produced a marked rise in mean plasma cortisol, from 64.2 micrograms/l to 164.5 micrograms/l.(ABSTRACT TRUNCATED AT 250 WORDS)