Previous studies have shown that under free-feeding conditions, TCDD-treated Han/Wistar (H/W) rats consume less sucrose solution but ingest more saccharin solution than their controls thus implying hyperresponsiveness to postingestive satiety signals. In this study, nutrient preloads were employed to further elucidate this phenomenon. Male H/W rats were given a single high but usually non-lethal intraperitoneal dose (1000 micrograms/kg) of TCDD. Feed intake was stimulated by 24 hr feed deprivation at various time points after TCDD exposure. When TCDD-dosed rats were allowed to drink either a 20% sucrose or a 0.25% saccharin solution and then given access to feed, those that had had sucrose ate only about 50% of the amount consumed by the saccharin group. Although the preloads were similar in control rats, no such difference in subsequent feeding occurred. The sucrose solution also produced a longer-lasting suppression of feed intake in TCDD-treated compared with control rats when infused directly into the stomach. By contrast, TCDD-treated H/W rats failed to exhibit an augmented satiety response to parenterally applied glucose independent of testing time. Oral corn oil reduced feed intake in both control and TCDD-exposed rats, but the inhibition was slightly larger in TCDD-treated animals. TCDD did not markedly affect the responsiveness of H/W rats to the suppression of feeding by CCK-8 or bombesin. It is concluded that gastrointestinal factors appear critical to the exaggerated response of TCDD-treated H/W rats to nutrient energy.