10 normal persons were given 0.4 milligrams of Naloxone intravenously, and the following measurements were taken: oxygen uptake, CO2 production, respiratory quotient, respiratory minute volume, tidal air, dead space, effective dead space, specific ventilation, alveolar O2 partial pressure, end-expiratory CO2 partial pressure, heart rate, systolic and diastolic blood pressure and the Burger Index. Analysis of the results established that administration of Naloxone was followed by a statistically significant, but clinically not relevant, reduction in O2 uptake and CO2 production. Higher doses produced the same results. The findings appear to contradict those observed in anaesthetised patients who are given Naloxone during the postoperative stage. However, closer examination of the results suggests that the so-called tachytrophic effect of Naloxone is attributable to its antagonistic action on the analgesic and sedative effects of opiates rather than to a specific pharmacodynamic property of Naloxone.