Rats often exhibit diet-induced thermogenesis when overfed, which has been linked to activation of the sympathetic nervous system. In the present study, adult dogs housed at 22 degrees C were fed 150 or 200% of maintenance intake for 4 wk or 6 d, respectively. The overfed dogs gained body weight without an increase in 24-h energy expenditure or activation of the sympathetic nervous system, as assessed by norepinephrine release to plasma and urinary norepinephrine excretion. Acclimation to cold (3 degrees C for 4 wk) increased energy expenditure 38%, norepinephrine apparent release to plasma 64% and urinary norepinephrine excretion 42%. This cold-induced thermogenesis did not, however, switch to diet-induced thermogenesis when dogs were removed from the cold and fed 150% of maintenance. In conclusion, no evidence was found for diet-induced thermogenesis in adult dogs.