WE describe quantitation of the absolute amounts of 5HT2Areceptor mRNA in various areas of human postmortem brain using a very sensitive and specific technique: competitive reverse transcription polymerase chain reaction (RT-PCR). With this procedure, we were able to show that the highest levels of 5HT2Areceptor mRNA are in cerebral cortical areas, i. e., Brodmann's areas 8, 9, 10, 18, 19, 22, 24, and 46, and that intermediate levels occur in the hippocampus, the amygdala, the nucleus accumbens, and the hypothalamus. Very low levels of 5HT2Areceptor mRNA were found in the cerebellum, the thalamus, the caudate, and the putamen. Our results confirm the heterogeneous distribution of 5HT2Areceptor mRNA in human postmortem brain and suggest that competitive RT-PCR is a highly sensitive and specific procedure for the quantitative measurement of 5HT2Areceptor mRNA expression. The study of 5HT2Areceptor mRNA in different brain areas will help clarify the regulation of 5HT2Areceptors at the transcriptional level in various neuropsychiatric diseases.