The paper outlines the results of following up 50 infants and preschool children who had contacts on their families. The major sources of infection were equally both their mother and their father. The children were found to have pronounced active processes. The most severe types of tuberculosis were common in infants in whom general, military tuberculosis and tuberculous meningitis along with complicated types in intrathoracic lymph node tuberculosis were detected. There was more commonly a phase of dissemination and decay in infants. Severe types of tuberculosis were encountered in the families having a combination of many unfavourable factors, both medical and social ones. Among the children who had fallen ill, 32% were detected on their visits to polyclinics of upon admissions to general hospitals.