To specify the influence of blood pressure on diabetic microangiopathy, the factors related to retinopathy and nephropathy were studied among 56 consecutive type 1 (insulin-dependent) diabetic out-patients without hypertension. Diabetes mellitus had been diagnosed for at least one year (mean duration of diabetes +/- SEM = 11.4 +/- 0.9 years). Diabetic patients did not take any treatment liable to influence blood pressure. Clinical parameters, including blood pressure, tobacco and alcohol consumption, were recorded by the same investigator. Retinopathy was defined as more than 5 microaneurysms on a fluorescein angiogram, clinical and incipient nephropathy as an albumin excretion rate over than 300 mg/d and between 30 and 300 mg/d, respectively. On average, retinopathy (n = 25) was associated with longer duration of diabetes (16.5 +/- 1.2 vs 7.4 +/- 0.9 years; p less than 0.001) and higher systolic blood pressure (136.2 +/- 4.1 vs 126.3 +/- 2.8 mm Hg; p less than 0.05). Clinical (n = 9) and incipient (n = 23) nephropathies were associated with duration of diabetes (17.9 +/- 2.0 and 11.8 +/- 1.7 vs 8.7 +/- 1.6 years, respectively; p less than 0.01), and with systolic (145.0 +/- 7.9, 132.7 +/- 4.7 vs 123.5 +/- 4.2 mm Hg; p less than 0.01) and diastolic blood pressure (83.3 +/- 6.2, 77.3 +/- 3.2 vs 72.2 +/- 3.4 mm Hg; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)