Abnormalities in the regulation of natriuretic peptides (NP) associated with major diseases such as hypertension, heart failure, and diabetes mellitus (DM) have been reported. We investigated levels of mRNA for the vasodilator C-type natriuretic peptide (CNP) in the renal cortex of streptozotocin (STZ)-diabetic rats and the influence of an angiotensin II inhibition.