We studied the expression of kidney renin gene in hypertensive animals by measuring the kidney renin messenger (m) RNA. The kidney renin mRNA was quantified by densitometric Northern biot analysis using a32P-labelled rat renin genomic DNA fragment as a hybridization probe. Spontaneously hypertensive rats (SHR) and control Wistar–Kyoto rats (WKY) were treated with a low-sodium diet plus furosemide, captopril or propranolol for a week. Plasma renin activity (PRA) in SHR and WKY was increased similarly by sodium depletion and by treatment with captopril. PRA in both strains was not decreased significantly by treatment with propranolol. Both sodium depletion and captopril treatment caused significant increases in the kidney renin mRNA in SHR and WKY. However, the increases in the kidney renin mRNA of SHR were greater than those in the corresponding WKY (SHR, 10.0− and 22.1-fold increases; WKY, 6.2− and 7.8-fold increases, respectively). Propranolol had no effect on the kidney renin gene expression in either WKY or SHR. These results indicate that SHR show an enhanced expression of the renin gene in the kidney compared with WKY in response to stimuli that increase renin release.