Atomic absorption spectrophotometric method was used to determine the serum selenium levels of 86 healthy individuals. Variations in age, sex, and geographically different urban regions of Yugoslavia were investigated. A group of 63 healthy children, ages 8-15 yr, were examined. Mean +/- standard deviation of the serum selenium concentration was 57 +/- 9-mu-g/L; age and geographic area had no effect on the Se status of children, but the difference between boys and girls was significant (P < 0. 05). A group of 23 men from Zagreb, ages 22-37 yr, were examined. The group was divided into three age subgroups and no difference was found among these groups. The mean Se concentration was 69 +/-18-mu-g/L, and a statistically significant difference was found only between the group of adults and the group of children (P < 0.05).