To determine the prevalence of increased urinary albumin excretion (UAE) in essential hypertension and to establish whether this abnormality is associated with deranged renal function, we have measured UAE in a group of 123 patients with essential hypertension and in 110 normal subjects. Mean arterial pressure (MAP) was 96 +/- 0.6 mm Hg in normal subjects and 121 +/- 0.3 mm Hg in patients with essential hypertension (p less than 0.01). Mean UAE was 8.6 +/- 0.5 in normal subjects and 32.9 +/- 3.3 mg/24 h in patients with essential hypertension (p less than 0.01). Forty percent of patients with essential hypertension manifested a UAE exceeding 30 mg/24 h and had an average UAE of 72.0 +/- 4.7 mg/24 h. MAP in patients with increased UAE was similar to that in subjects with normal UAE (121 +/- 0.5 vs. 121 +/- 0.4 mm Hg). Creatinine clearance was also not different between these two groups (91 +/- 1.8 vs. 94 +/- 1.5 ml/min). No correlation was found between UAE and MAP or creatinine clearance. Long-term prospective studies are needed to extablish whether an increase in UAE may predict future nephrosclerosis in essential hypertension.