Low-protein (LP) feeding (6%) of rats results in renal hemodynamic changes that are abolished by converting enzyme and nonpeptide AT1 inhibitors, suggesting a role for intrarenal angiotensin II (ANG II). Dietary protein is a stimulus for the expression of renal renin mRNA in intact and partially nephrectomized rats. In the present study, LP increased renal renin immunoreactivity and renin mRNA as assessed by in situ hybridization and Northern blot analysis; whole kidney expression of angiotensinogen mRNA was unaltered. Whole kidney, cortical, and medullary ANG I-converting-enzyme (ACE) mRNA was also increased in LP vs. normal protein. The changes occurred despite a reduced protein synthetic rate (RNA-to-DNA ratio) in the kidney of LP, which did not change expression of renal glyceraldehyde-3-phosphate dehydrogenase mRNA. These studies show for the first time that LP diet increases the expression of renal renin and ACE mRNA in intact rats; these may be responsible for the renal hemodynamic changes of LP.