We measured urinary albumin excretion in 2,224 school-children (1,168 boys, 1,056 girls) aged 2-18 years, between 1989 and 1990 to establish reference values. We recorded all pathological antecedents and findings from physical examination, including anthropometric parameters and arterial blood pressure. The analytical study included serum total protein, albumin and creatinine. The second-morning urine and the nightly (rest) 10-h urine sample were collected and we determined the concentration of albumin and creatinine. We found a positive statistically significant correlation between the urinary albumin excretion (micrograms/10 h) and age, height, weight and body surface area. We suggest that it would be useful to relate the urinary albumin excretion to body surface area. The mean value for albumin excretion was 3.49 micrograms/ml in boys and 3.63 micrograms/ml in girls. The urinary albumin/creatinine ratio showed a high correlation with the albumin excretion (r = 0.958).