The present study was designed to characterize the hypophagia that is a salient feature of the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced wasting syndrome. When TCDD-treated Long-Evans (L-E; dose 50 micrograms/kg) and Han-Wistar (H-W; 3000 micrograms/kg) rats were offered a simultaneous choice of three diets differing in their macronutrient composition, no selective aversion was seen to any of the varieties, although total energy intake decreased drastically and especially so in L-E rats. Further studies in H-W rats showed that TCDD treatment leads to a permanent retardation of weight gain accompanied by a decreased intake of chow and of a 10% sucrose solution, and to a reduced or unchanged consumption of water. In contrast, there was a progressive increase in saccharin drinking (when offered as the only choice) in TCDD-dosed rats with time. TCDD-treated animals also tended to consume a greater proportion of their daily feed intake during the daytime. These results imply that TCDD induces aversion to eating energy-providing food, irrespective of its type, and that TCDD exerts this at least in part by sensitizing the rats to post-ingestive satiety factors.