A variety of evidence indicates that neurotensin may be involved in the regulation of ingestive behavior. Cerebral ventricular injections of this peptide produced a dose-dependent decrease in the food intake of food-deprived rats. The duration of the aphagia was found to be approximately 90 minutes for the highest dose employed (100 micrograms). The possibility that tolerance might develop to the aphagic effect of neurotensin was investigated. No evidence of tolerance was found after 6 consecutive days of ventricular injection. In addition to ventricular injections, 2 possible central sites of action were examined: the ventromedial nucleus of the hypothalamus and the nucleus accumbens. While microinjections of neurotensin into the nucleus accumbens did not alter food intake, ventromedial hypothalamic administration resulted in a dose-related reduction in food intake. The results are discussed in relation to the possible role of central nervous system neurotensin in the control of feeding.