Age-related changes in the blood concentrations of glycated proteins during childhood and adolescence were examined by measuring the blood fructosamine (FA), glycated albumin (GA), glucose levels and total serum protein levels in 611 healthy children (325 boys and 286 girls) aged 0-18 years old. These levels were compared with those of 130 healthy adults. GA was measured by a newly developed, highly precise method of high-performance liquid chromatography (inter-assay coefficient of variation, 4.9%). The FA values of all groups of up to 15 years old (grouped in two year age brackets) were significantly lower than those of adults. The mean serum concentrations of GA in infants up to four years old were also significantly lower than in adults. A slight but statistically significant positive correlation was found between age and values of FA (r = 0.36, P less than 0.001), but not of GA (r = 0.04). Levels of total serum proteins showed a positive correlation with those of FA (r = 0.47, P less than 0.001) but a weak correlation with those of GA (r = 0.29). These results suggest that age should be taken into account when the FA levels of children and the GA values of infants are evaluated.