Characteristic features of subjects of the VIA registration group (500 children and adolescents) observed by one of the Moscow children's polyclinic from 1983 to 1987 are given. The rate of primary contamination amounted to an average of 0.75% a year. 92.8% of children and adolescents were infected as a result of an unknown contact, while 7.2% of them had contact with relatives suffering from tuberculosis. In case of conversion of tuberculin reactions, hypersensitivity to tuberculin was seen in 12.2% of the patients and a year later in 4.6% the subjects with persistent hyperergy who were then transferred to the VIB registration group. The following risk factors of contaminating and contacting tuberculosis were found: contact with tuberculosis patients; immunization of poor quality or its absence; hypersensitivity to tuberculin; frequent acute respiratory viral infections and chronic diseases; and unfavourable social and living conditions. The number of these factors should be taken into account since with their growth, the rate of hyperergy and risk of developing the disease are higher. More thorough examination and controlled preventive chemotherapy at a sanatorium are required when 2 or more risk factors are available.