In order to examine the existence and level of androgen receptor messenger ribonucleic acid (ARmRNA) in the rat brain, reverse transcription-polymerase chain reaction (RT-PCR)-Southern blot analysis was carried out. Total RNA extracted from each tissue was reverse transcribed, followed by PCR with two oligonucleotide primers specific for a part (458bp) of the androgen binding domain of the rat ARcDNA. It was confirmed by direct nucleotide sequencing that the amplified fragment corresponded to part of the rat ARcDNA. To detect and quantify the amplified fragments, a Southern blot analysis was carried out. The levels of amplified fragments were calculated from the standard curve obtained from graded diluted adrenal total RNAs. In the present study, it was revealed that the RT-PCR-Southern blot analysis possessed a high-degree of sensitivity and allowed the quantitative estimation of mRNA. With this method, amplified fragments were obtained from all five brain regions examined. The results indicate that ARmRNA is widely distributed in the whole brain. Moreover, since the ARmRNA level roughly paralleled the AR protein level, it seems that the AR protein level in the brain may be primarily regulated by the ARmRNA level.