A genomic renin exon 9 fragment was subcloned into vector pSPT18 and used for in vitro transcription to obtain ³²p-labeled rat renin cRNA. Using this cRNA, we established quantitative solution hybridization and specific Northern blotting assays for renin mRNA. We were able to detect renin mRNA in the kidney, heart ventricle and atrium, brain, testis, and adrenal gland of male rats in the concentrations of 430±8.1, 110±1.9, 43±0.9, 64±1.1, 47±0.9 and 11±0.2 pg mRNA/mg of total RNA, respectively.