Urinary albumin excretion (UAE) was determined by radioimmunoassay in two 24 h urine collections from 125 diabetic children and adolescents and from 71 normal children matched for age and sex. Thirteen patients (10.4%) aged greater than 12 years had microalbuminuria, i.e. log transformed UAE levels above the upper normal range (24.5 mg/24 h). UAE values were positively correlated with age, GH secretion, but not with duration of disease, glycosylated hemoglobin, renal size or N-acetyl-beta-glucosaminidase excretion. Diabetic normoalbuminuric children aged 10 years and older had significantly higher UAE than controls and than younger diabetic patients matched for duration of disease. HLA DR3/DR4 heterozygosity frequency was significantly higher (p less than 0.01) in the microalbuminuric group than in the normoalbuminuric. All microalbuminuric subjects (n = 8) with short duration of disease (3.92 +/- 3.43 yr) developed diabetes at puberty. In conclusion, our cross-sectional study suggests: if a number of factors are combined, i.e. HLA DR3/DR4 heterozygosity, onset of disease at puberty and higher GH values, the probability of developing abnormal levels of UAE will increase.