The aim of this study was to define normal values of albumin excretion rate (AER) in young people. We measured overnight timed AER (tAER, microgram/min) by a double-antibody radioimmunoassay in 281 healthy Italian children and adolescents (160 M and 121 F), aged 7-19 years. The frequency distribution of tAER deviated from normality, therefore percentiles were used: median and 95th percentile were 2.3 and 6.9 micrograms/min respectively. Log transformed tAER was not related to age or pubertal stage. "Borderline" AER refers to AER higher than normal 95th percentile in non-diabetic subjects but lower than microalbuminuria threshold level. Incipient nephropathy, expressed as "borderline" AER, has been reported in adult IDDM patients, and can be reversed by improving metabolic control. Because incipient diabetic nephropathy may be present in young IDDM patients without microalbuminuria, screening for AER should be recommended for pediatric diabetic patients, also before puberty, in order to detect early renal damage and the "borderline" AER state.