The calorigenic action of circulating epinephrine was analyzed quantitatively in the dog during pentobarbital, halothane and morphine anesthesia. The whole body oxygen consumption (VO2) was measured by an on-line analysis of breath-by-breath respiratory gas exchange. Epinephrine was infused at various doses and the plasma concentrations of epinephrine were measured by semiautomated fluorimetric analysis. During pentobarbital anesthesia, the basal VO2 was 5.26 ml/kg/min and was increased by epinephrine in a dose dependent manner at plasma concentrations between 3.9 ng/ml (VO2 = 5.68 ml/kg/min) and 36.5 ng/ml (VO2 = 6.47 ml/kg/min). Epinephrine exerted a similar effect during halothane anesthesia, but it failed to affect VO2 during morphine anesthesia. Morphine also inhibited dibutyryl cyclic AMP-induced increase in VO2, suggesting that morphine inhibits the calorigenic action of epinephrine at the intracellular site distal to beta-receptors.