Discovery of two cases of infectious tuberculosis in a state prison in 1976 prompted a careful study of the entire population of 1,500. Eight more cases were found, giving a morbidity of 670/100,000 (arkansas rate, 21.1). The epidemic was aborted by the use of isoniazid and the establishment of a program for screening and periodic retesting. Clear evidence was found for intramural spread of the infection, and eight of 16 persons with clinical tuberculosis from 1975 to 1977 had entered the prison uninfected. Nine percent of 800 men with tuberculosis in Arkansas from 1972 through 1977 had "done time" in this particular prison. In January 1978 a child died of tuberculosis transmitted from a former inmate who had been infected while incarcerated in 1976 but released without therapy. Tuberculosis morbidity was 6.5 times greater in state prisons than in the general population.