The study was conducted prospectively and retrospectively in three groups of patients: intravenous drug users and their sexual contacts in an already-recruited cohort; children who received their primary care at Bellevue Hospital Medical Center; and Bellevue Hospital Center inpatients with TB and outpatients who underwent prophylactic treatment. In addition to environmental risk factors (e.g., hopelessness, cohabitation with tuberculosis patients and injected drug use), host factors were investigated, including: HIV infection; immune status among HIV- seropositive persons, as indicated by quantitative p24 antibodies; CD4, CD8, and gammadelta T cell counts; and race, age, and nutritional status. Incidence and risk-factors in the cohort were assessed by interview, blood draw, PPD screening, medical record review, and anergy panel. Natural history and impact on HIV disease in adult and pediatric populations were assessed by interviews, clinical screening and laboratory measures. Drug sensitivity testing and RFLP typing of specimens from the two populations were conducted, respectively, at the Bellevue Mycobacteriology Lab and the Public Health Research Institute. Factors affecting treatment compliance were assessed by self-administered questionnaire.