In the group of 26 schoolchildren (11 girls and 19 boys) coming from an area with strong air-pollution the venous blood and saliva were taken before and three weeks after the sojourn in the countryside school environment. The mean levels of IgG and IgA in serum significantly rose during the sojourn, but the IgM levels increased insignificantly only. The mean levels of alpha 1-antitrypsin and alpha 2 macroglobulin significantly decreased, whereas the levels of transferrin increased significantly. Subnormal values in individual tests were estimated at 38 percent of children before the sojourn, but at the end of the sojourn only 11.5 percent of children remained subnormal. The values over the upper limit of normal were, before the sojourn assessed, at 11.5 percent of children in some of the tests, whereas 53.8 percent were found after the sojourn. The results are discussed from the point of view of a stimulating influence on the resistance mechanisms during the sojourn in the unpolluted area.