Two phases in postprandial thermogenesis have been recently identified in dogs; an initial cephalic phase lasting 45 min and a subsequent digestive phase occurring after 45 min. The objective of this study was to determine the role of the autonomic nervous system during these two phases in dogs. O2 uptake (VO2) as well as respiratory quotient (RQ) were monitored at least 1 h before and 2 h after a meal of 1,034 kcal under the following infusion conditions: saline, propranolol, atropine, propranolol plus atropine, phenoxybenzamine, and propranolol plus phenoxybenzamine. The initial peak value for VO2 increase was 100% in the cephalic phase and 40% in the digestive phase during the saline infusion. The VO2 response during the initial phase was 58 and 56% less with propranolol and atropine, respectively, compared with the control experiment. A 36% decrease in the VO2 response was found during the digestive phase with propranolol, whereas it was abolished by atropine. Propranolol and atropine given together decreased the VO2 response during the cephalic phase by 27% and abolished it completely in the digestive phase. Phenoxybenzamine did not affect the VO2 or RQ responses during the whole period and when given in combination with propranolol the same result as propranolol alone was found. These findings indicate that both the parasympathetic and sympathetic nervous system participate in the control of postprandial thermogenesis during both the cephalic and digestive phases.