Neurotensin (NT) is widely distributed in the central nervous system (CNS) and peripheral tissues, and its actions are mediated by a specific family of G protein-coupled receptors. In this study, the authors have measured the levels of gene expression of the high-affinity neurotensin receptor (NTR) with quantitative reverse-transcriptase-polymerase chain reaction (RT-PCR). In the rat brain, the highest quantities of NTR mRNA were found in the ventral mesencephalon and in the hypothalamus. Surprisingly, almost identical quantities were detected in both structures, despite results from in situ hybridization studies revealing a low expression of NTR mRNA in the hypothalamus. The RT-PCR data suggest that large scale NTR mRNA synthesis is occurring in restrictive hypothalamic nuclei. Intermediate levels of expression were detected in the prefrontal cortex and striatum, and scant levels in the cerebellum. In peripheral tissues, the highest levels of NTR mRNA were detected in the colon, followed by the liver, and then duodenum and pancreas. In this study, the sensitivity and the accuracy of the quantitative RT-PCR method provided the means to estimate the relative distribution of NTR mRNA between brain structures and peripheral tissues. Therefore, this study promotes a better understanding of the localization of NTR synthesis in relationship with the various physiological effects of NT.