At present we are able to disclose diabetic nephropathy in the very early stages, i.e. when urinary albumin excretion is only slightly increased (20-200 micrograms/min = microalbuminuria). Good blood glucose control and active antihypertensive treatment may stop or retard the further development towards renal failure. Angiotensin-converting-enzyme (ACE)-inhibitors seem to have a renoprotective effect. In this article we suggest guidelines for the use of ACE-inhibitors in patients with type 1 diabetes and early diabetic nephropathy. Special concerns are included in respect of adolescents, pregnant women and persons with type 2 diabetes.