Using hybridization histochemistry renin gene expression has been localized in the juxtaglomerular apparatus (JGA) of the renal cortex in both mouse and sheep kidney. This technique also located renin gene expression in afferent arterioles and interlobular arteries distant from the glomerular tuft in lamb renal cortex. A short (30 mer) synthetic oligonucleotide probe, complementary to a region of the mouse submaxillary gland renin gene, specifically labelled mouse submaxillary gland and kidney. Hybridization histochemistry and Northern blot analysis using both the synthetic oligonucleotide (mouse) probe and a 700 base pair recombinant (sheep) probe showed differences in renin gene expression in the kidney in response to Na restriction in the mouse and Na depletion in the sheep.