Blood serum selenium levels were measured in 891 healthy children and adolescents (aged 11-18 yr, 450 girls and 441 boys) residing in both rural and urban areas from eight regions of Slovakia. Subjects were divided into four age groups (11-12 y, 13-14 y, 15-16 y, and 17-18 y). Serum selenium concentration was determined by the electrothermal atomic absorption spectrometric method. The mean (+/-SD) serum selenium concentrations were 0.750 +/- 0.255 mu mol/L in girls and 0.773 +/- 0.235 mu mol/L in boys. A large proportion of the individuals (25.7% in girls, 18.1% in boys) exhibited serum selenium levels under 0.57 mu mol/L (45 mu g/L). An increasing trend of the serum selenium values with age has been observed in both boys (p < 0.01) and girls (p < 0.05). Boys had higher serum selenium levels in the all age groups but the differences were not statistically significant.