Messenger ribonucleic acid (mRNA) from mouse brain was reversely transcribed and complementary deoxyribonucleic acid (cDNA) encoding transmembrane domains (TM) 3 through TM6 of the thyrotropin-releasing hormone receptor (TRH-R) could be amplified by polymerase chain reaction (PCR). The partial cDNA of TRH-R was identical to that of the pituitary in size and sequence. The regional distribution of reverse transcription PCR products (partial cDNA of TRH-R) was similar to that of TRH-Rs themselves, except in cerebellum where TRH-R mRNA levels were relatively higher than the levels of TRH-Rs themselves previously reported.