Postprandial thermogenesis is under the control of the autonomic nervous system and alimentary conditioned stimuli change sympathetic and parasympathetic activity. Here we studied the effect of conditioned taste aversion on postprandial thermogenesis in rats. Two groups of animals were used, rats of the first group were controls, these were placed on a standard diet and, for some days, on two other different diets: one thiamine-free and the other thiamine-rich. Each diet had a different taste. The treated animals belonged to the second group, these were fed with the same three diets but for different lengths of times: thiamine-free diet for the first 5 wk afterwards, with thiamine-rich diet for 3 wk, and finally with laboratory standard diet for a few days. After a preference test with the three familiar diets, oxygen consumption rate and brown adipose tissue temperature were evaluated three times in both groups after ingestion of a test meal, each time with one of the three different diets. The preference test was unvaried for the three different familiar foods in controls, while the treated animals showed a lower preference for thiamine-free food than for the other two. Treated rats had a significantly higher increase in O2 consumption rate than controls. In this group intake of thiamine-free food induced a significantly lower increase in O2 consumption than the other two. The increase in brown adipose tissue temperature was also higher in treated than in control animals but in treated rats this was lower after intake of thiamine-free food than after the intake of the other two.(ABSTRACT TRUNCATED AT 250 WORDS)