Points of agreement: (1) In IDDM, hypertension occurs in patients who have already developed nephropathy, probably in the microalbuminuric phase. (2) Hypertension is an important accelerator of the development of diabetic nephropathy. (3) Hypertension, obesity and NIDDM are often associated, and insulin resistance is commonly observed in all three states. (4) Antihypertensive therapy retards the development of diabetic nephropathy in IDDM and reduces proteinuria in NIDDM. (5) The choice of antihypertensive agent in the diabetic patient must be based upon the efficacy of the drug as well as avoidance of side effects including deleterious influence on glucose, insulin and lipid levels and renoprotection. (6) Carefully conducted long-term comparative trials between different classes of antihypertensive drugs in microalbuminuric IDDM and NIDDM patients are essential. Points of major controversy: (1) Detection of IDDM patients prone to the development of diabetic nephropathy can be performed by measuring specific parameters such as erythrocyte Na(+)-Li+ countertransport activity. (2) Insulin resistance is a pathogenic mechanism rather than purely an association with hypertension and obesity. (3) A certain class of antihypertensive agents--ACE inhibitors--confers a specific renoprotective effect in diabetic nephropathy, in addition to its effects upon systemic blood pressure. (4) Reduction of blood pressure should be considered in the normotensive microalbuminuric diabetic patient. (5) Microalbuminuria is a sufficient 'surrogate endpoint' for the progression of renal failure.