Antagonistic effect of naloxone was tested in two kinds of total anesthesia. In one group the preparation was tested in ten experimental dogs with neuroleptanalgesia induced by the simultaneous intramuscular application of chlorpromazine (3 mg/kg) and piritramide (4 mg/kg). After 60 minutes naloxone was applied i. m. at a dose of 0.2-0.4 mg pro toto to reverse the anesthetic effect. In another group of 15 dogs - clinical patients - the effect of naloxone was evaluated in analgesia induced by i. m. application of piritramide at a dose of 3 mg per kg with atropine premedication (0.05 mg per kg). After a surgical operation, lasting in particular cases 20-45 minutes, the same dose of naloxone was applied i. m. as in the first group to reverse the anesthetic effect. In both groups of animals naloxone application caused a reverse of the anesthetic effect of piritramide and in the first group a statistically significant reverse of the inhibition of breathing and heart action.