This final report compared the efficacy of four 6-month chemotherapy regimens 30 months after the completion of treatment. All patients received isoniazid, rifampin, and ethambutol daily in hospital for the first 8 wk of treatment. One group continued to receive these 3 drugs daily as outpatients for an additional 18 wk; a second group received the same drugs twice-weekly, and a third group received the 3 drugs once-weekly during the 18-wk "continuation phase." A fourth group of patients received 2 drugs, isoniazid and rifampin, twice-weekly during the continuation phase. Drug toxicity was not a major problem; drugs were permanently discontinued in only 1% of the patients. All 4 regimens were highly effective in achieving sputum negativity. However, the relapse rate was found to be relatively high for all regimens (range, 8 to 22%).