The rate of free radical reactions is one of stress markers. The ability of the organism to resist oxidation is determined by various factors, including vitamin supply. Vitamins A, E, C and group B vitamins directly or indirectly affect the degree of antioxidant protection. We have studied vitamin supply in school children aged 12 to 17 in urban (n = 250) and rural areas (n = 200) and the rate of free radical reactions in their blood serum by induced chemiluminescence. Deficiency of vitamins A and E, which have antioxidant properties, was detected in both urban and rural school children; however, the former had a higher deficiency level. This corresponds to the chemiluminiscence assay data: all chemiluminescence assay values in urban school children were 2.2–7.6 times higher than in rural school children, which indicates a higher intensity oxidation in their bodies. A deficiency of group B vitamins was also detected in rural school children, riboflavin being an exception in a subgroup of 15 to 17 year old subjects.