ABSTRACT:In order to study the role of the renin‐angiotensin system in patients with diabetic nephropathy, renin release and the juxtaglomerular apparatus were studied in 17 diabetic patients with proteinuria and in 23 without proteinuria; 8 normal subjects were used for controls. Despite hypertension and marked arteriosclerosis, plasma renin activity (supine posture) was normal; however, the renin response to salt restriction and upright posture was less in the diabetic patients with proteinuria than in the controls. Renal renin content, determined at autopsy, was also normal. Examination of the juxtaglomerular apparatus in the diabetic patients with proteinuria revealed hyalinization of the afferent and efferent arterioles in most of the glomeruli and various degrees of destruction of the juxtaglomerular cells. The findings suggest that renin production is not increased in diabetic patients with proteinuria plus marked vascular damage, and that the renin‐angiotensin system in patients with diabetic nephropathy apparently does not play an important role in the exacerbation of hypertension or the degree of vascular dam