The 5' flanking region of the human renin gene contains two putative promoter sequences (TATA boxes), named P1 and P2. These are located in positions -77 to -71 and -29 to -23 respectively, each followed by a possible translational start site (AUG). In order to identify whether these sequences are functional in the kidney, we employed the RNAse protection assay. Total RNA extracted from human kidney cortex was hybridized with labeled cRNA probes complementary to the 5' flanking region of the human renin gene. After digestion with RNAse, protected hybrids were identified by electrophoresis on polyacrylamide/urea gels and autoradiography. Results showed that only P2 is active in human kidney resulting in a single transcript. This suggests that human kidney renin is synthesized as a single preproform.