We and others have reported elevated levels of renin mRNA in extrarenal tissues of the spontaneously hypertensive rat (SHR) of the Okamoto strain. We hypothesise that this is due to mutations we have found in putative, cis-regulatory regions in the first intron of its renin gene. Here we report two G-A mutations at position +502 and +934 of the first intron of the SHR renin gene, when compared to normotensive Wistar Kyoto (WKY) and Sprague Dawley (SD) rats. These mutations fall within consensus sequences for the well described E2A and peroxisome proliferator-activated receptor (PPAR) transcription factors. We used electrophoretic mobility shift assays to determine if these mutations alter the pattern or affinity of nuclear protein binding to oligonucleotides homologous to these regions of the renin gene. Both mutations significantly altered the intensity and pattern of nuclear protein binding to oligonucleotides homologous with the renin gene regions bearing these putative transcription factor binding sites. Thus these mutations have the potential to alter the type and/or affinity of transcriptional factors for the SHR renin gene in vivo, and result in renin overproduction at an extra-renal tissue site subserving blood pressure control.