A carboxy terminal renin complementary DNA (cDNA) clone from rat kidney was isolated, characterized, and used as a probe for renin messenger RNA (mRNA) quantification in normotensive and hypertensive rats. RNA blotting analysis detected renin mRNA in control kidney and brain. Deoxycorticosterone acetate (DOCA) and high salt (1 %) treatment of experimental gnimnls resulted in a greater than 95% decrease in the content of renin mRNA in the kidney, as compared with values in control rats receiving 0.4% NaCl in their diet. In contrast, high salt (1%) treatment alone caused only a twofold decrease in kidney renin mRNA content, as compared with values in controls. DOCA and low salt (0.04%) or low salt (0.04%) treatment alone caused a 1.5-fold Increase in the kidney renin mRNA content, as compared with values in control rats. These results indicate that DOCA and salt have a synergistic effect in depressing renin mRNA levels in kidney. Clipping of the left renal artery caused a threefold increase in the steady state level of renin mRNA in the iscbemic kidney and a 0.5-fold decrease in the hypertrophied kidney. The data are consistent with the hypothesis that blood pressure and other stimuli regulate the expression of the renin gene in vivo.