Reference intervals for urinary albumin were determined for adults (n = 358) using second morning urine (spontaneous). Percentiles were as follows: 90th percentile: 18 mg/l or 16 mg/g creatinine. 95th percentile: 28 mg/l or 24 mg/g creatinine. When related to volume, albumin values of children aged from 3 to 5 years (n = 60) were in the same range. When related to urinary creatinine, however, significantly higher values were obtained. The preliminary upper reference limit is 30 mg/g creatinine.