To ten male volunteers, 25 to 35 years old and without any known disease, physiological saline solution (placebo) 1 ml, morphine 10mg, and Remeflin 16 mg were administered intramuscularly. Effects of tbese agents upon ventilation at rest and respiratory response to carbon dioxide rebreathing were studied. The results are as follows: 1) Morphine significantly decreased respiratory rate, minute volume, and Pao₂ and increased Paco2 without significantly affecting either tidal volume or arterial pH. 2) In morphine-induced respiratory depression, Remeflin improved ventilation by significantly increasing tidal volume and minute volume with resultant increase in Pao₂ and decrease in Paco2, Remeflin did not significantly alter respiratory rate and arterial pH 3) Morphine displaced respiratory response curve to carbon dioxide obtained with placebo 7 torr to the right and Remeflin 6 torr to the left. No changes in slope of the curves were observed. 4) It is concluded that Remeflin stimlulatea respiration by directly acting upon the respiratory center.