1. Twenty-four hour urinary albumin excretion rate was measured by a sensitive radioimmunoassay in 99 male and 100 female randomly selected factory workers, aged between 20 and 60 years. 2. The median (range) albumin excretion rates for men and women of 4.67 (1.0-25.8) and 5.25 (0.2-33.0) mg/24 h, respectively, were not significantly different. 3. No correlation was established between diastolic, systolic or mean arterial blood pressure and albumin excretion rate for the whole group. 4. Twenty-eight subjects with systolic and/or diastolic blood pressures greater than or equal to 140/90 mmHg (18.7/12.0 kPa) showed a positive correlation between mean arterial blood pressure and albumin excretion rate (r = 0.412, P less than 0.01). 5. There was no significant relationship between number of cigarettes smoked, age or alcohol intake and albumin excretion rate. 6. The data suggest that in the general population albumin excretion rate is variable and not dependent on blood pressure, but at blood pressures greater than 140/90 mmHg (18.7/12.0 kPa) albumin excretion rate may become pressure dependent, although high albumin excretion rates were sometimes found in subjects with blood pressures less than 140/90 mmHg (18.7/12.0 kPa).