The comparative study of clastogenic and anticlastogenic activity of blood plasma in healthy children and children with bronchial asthma is performed. Clastogenic activity of whole blood plasma and 50% plasma of healthy children and children with bronchial asthma is reliably different from spontaneous mutations level as opposed to the level of aberrations induced by 25% blood plasma of healthy children and children with bronchial asthma. The analysis of genoprotective activity showed that blood plasma of children with bronchial asthma has lower ability to reduce the level of abberations induced by ethylmethanesulphate, than blood plasma of healthy children. Anticlastogenic activity of blood plasma of children with bronchial asthma being lower than in healthy children indicates the decrease of activity of antimutagenic blood system in remission period in the presence of normal level of total IgE.