An inherited predisposition to hypertension may increase susceptibility to nephropathy in type I diabetes. We evaluated the influence of a family history of essential hypertension on albuminuria in normotensive, normoalbuminuric type I diabetic patients. Forty-two diabetics (12.9 +/- 2.04 years) were divided into three groups according to tertiles of albumin excretion rate (group 1, 1.27 +/- 0.35; group 2, 2.43 +/- 0.49; group 3, 6.37 +/- 3.43 micrograms/min; P < .001). Familial hypertension was considered to be present if the patient had one parent or grandparent on antihypertensive therapy. The three groups did not differ concerning age, diabetes duration, insulin requirement, body mass index, blood pressure, and urinary glucose excretion. Albumin excretion rate did not correlate with any parameter studied. The frequency of hypertension was significantly lower among the relatives of the patients from group 1 compared with those from groups 2 and 3 (28.6% versus 64.3% versus 78.6%, P < .03). Our data suggest that a familial antecedent of hypertension in normoalbuminuric type I diabetic patients is associated with a high normal albumin excretion rate not related to increases in blood pressure. Early changes in renal hemodynamics, seen in patients with a predisposition to hypertension, may contribute to increments in albuminuria even within the normal range.