A study was performed to assess the risk of drug-dependent persons for developing tuberculosis. Tuberculosis prevalence was 3740/100,000 drug-dependent inpatients compared with 584/100,000 non-drug-dependent discharges. In another program, prevalence was 3750/100,000; in the New York [USA] Methadone Program, prevalence was 2652/100,000 patients in Harlem and 1372/100,000 city-wide. The city-wide prevalence rate in the entire population was 86.7/100,000 in 1971 and 64.7/100,000 in 1973. Similar elevations in incidence also were found in drug-dependent vs. non-drug-dependent populations. That the disease rate is elevated in drug-dependent populations suggests that drug dependency reflects a high-risk situation for tuberculous infected individuals developing tuberculosis disease. Infected drug-dependent persons (tuberculin positive) should be considered for preventive therapy with isoniazid, which can be piggybacked onto a drug treatment program.