In insulin-dependent diabetics the course of the renal disease can be followed by measuring arterial blood pressure and urinary albumin excretion. Already at the stage of incipient nephropathy (microalbuminuria) a moderate but gradually increasing rise in blood pressure is noticeable. At the stage of patent nephropathy (macroalbuminuria) nothing but an effective antihypertensive treatment can slow down the deterioration of renal function and delay by a few years the occurrence of end-stage renal failure. When macroproteinuria or obvious arterial hypertension are present, it is much too late to institute an antihypertensive treatment. To really prevent diabetic nephropathy, this treatment must be given earlier, as soon as microalbuminuria is detected and irrespective of blood pressure values. Prescribing antihypertensive drugs, and especially angiotensin-converting enzyme inhibitors, seems to be the most effective way of reducing urinary albumin excretion. 6