1. Neurotensin binding to synaptosomes isolated from the rat cerebral cortex and corpus striatum reached saturation after 4 min of incubation. 2. The rates of binding were found to be higher in the corpus striatum than in the cerebral cortex. 3. Concentration study revealed the presence of two different and independent classes of neurotensin binding sites with a negative cooperative interaction within each class of binding sites. 4. At saturation levels, the low affinity binding component was found to have a flat regional difference, while the high affinity binding component showed regional differences in terms of maximal binding capacity, suggesting a higher number of high affinity binding sites in the striatum than in the cortex. 5. In the competition related experiments, dopamine was found to displace around 70% of neurotensin binding sites in the corpus striatum and the cerebral cortex. 5. Substance P displaced around 50% of [3H]neurotensin in the cerebral cortex. Whereas, 50% and 70% displacement were observed in the striatum at high and low affinity binding sites, respectively. 6. These results show the overlap in the binding sites of neurotensin, dopamine and substance P.