Increased urinary albumin excretion rate (UAER) especially in the range of 20-200 micrograms min-1, termed microalbuminuria, has been proposed as a risk marker and predictor for cardiovascular disease in non-diabetic subjects. Thus it would be of importance to describe the distribution of UAER in the non-diabetic population. Among 1011 30-70-year-old subjects without diabetes mellitus or urinary tract infection, who were invited to participate in a population based epidemiological study, the albumin concentration was measured in an overnight urine sample. The measurement was performed by an ELISA method. The UAER was calculated in units of micrograms min-1 as urinary albumin concentration x urine volume/urine collection time. The distribution of UAER was positively skewed with a median value of 2.3 micrograms min-1 and a 5-95 interpercentile range of 0-11.0 micrograms min-1. The UAER held constant with age, but males had higher UAER than females, 2.6 (0-13.5) micrograms min-1 vs 2.2 (0-8.3) micrograms min-1; p < 0.005. The prevalence of microalbuminuria, defined as an UAER in the range of 15-150 micrograms min-1 in an overnight urine sample, was 3% (95% C.I. interval: 1.9-4.0). These findings suggest, that the level of UAER which might notify increased cardiovascular risk, is lower than in patients with diabetes mellitus, if it is considered to be of any clinical relevance.