In some countries extensive research is carried out on preventing tuberculous disease by administration of INH. In GDR since about 1960 chemopreventive measures were taken in cases of silicosis and silicotuberculosis too. More than 2000 patients of the Magdeburg Pneumoconiosis Center were followed-up from 1960 to 1969. The high risk of tuberculous disease of 21% in the group of silicosis patients without administration of INH could be reduced to 14% after preventive administration of INH. However, such clear effects were observed only under optimal conditions, that is sufficient dosage, duration and reliability of treatment. On the base of these results and other publications patients with silicosis with and without tuberculous residues should be included into the programmes of preventive chemotherapy of the chest clinics.