Large-scale trials with angiotensin converting enzyme (ACE) inhibitors and angiotensin II type 1 (AT(1))-receptor blockers have clearly shown that blockade of the renin-angiotensin system reduces the deterioration in renal function associated with diabetes. AT(1)-receptor blockers represent a more rational approach to blockade of this system than ACE inhibitors, due to the presence of non-ACE pathways of angiotensin II formation. Studies in healthy volunteers maintained on a low-salt diet indicate that such pathways account for approximately 30-40% of total angiotensin II formation, and this figure increases to 60-70% in individuals maintained on a high-salt diet (resembling the situation in most human populations). Activation of the renin-angiotensin system is increased in diabetic patients, and comparison of the renal vascular responses to captopril and candesartan shows a strong correlation between the effects of ACE inhibition and AT(1)-receptor blockade, indicating that the deleterious effects of renin-angiotensin system activation in diabetes are mediated largely through angiotensin II. The presence of multiple risk factors, such as genetic predisposition, hyperglycaemia, obesity and tissue damage, places diabetic patients at high risk of disease related to activation of the renin-angiotensin system. Effective and early blockade of this system is therefore an important aspect of management.