In order to clarify suppressive effects of mazindol (MZD) on food intake, its temporary or chronic infusion into the third ventricle was carried out. Changes in feeding patterns and endogenous chemical substances were determined following one shot infusion of 0.03 μmole MZD, as well as chronic infusion of 0.07 umole/day MZD using Alzet Minipump (Alza Corp.). MZD decreased meal size (MS) and increased postprandial intermeal interval (IMI), which led to enhanced satiety ratio (SR = IMI/MS) during only 4 hours following one shot infusion. On the other hand, chronic infusion of MZD continued to reduce food intake during 24 hours to the same extent as did one shot infusion. As for assaying of chemical substances in the plasma of fasted rats, MZD elicited a relative increase of glucose without hyperinsulinemia as well as a relative decrease of free fatty acids. These results were compatible with endogenous chemical changes in satiated states. Taken together with these findings, it was suggested that MZD reduced food intake, inhibiting the neuronal activities in the lateral hypothalamic area and/or accelerating those in the ventromedial hypothalamus.