In a study in Singapore, patients of Chinese, Malay, or Indian ethnic origin with sputum-smear-positive pulmonary tuberculosis received 2 months of daily treatment with streptomycin, isoniazid, rifampin, and pyrazinamide followed by daily isoniazid and rifampin, either with or without pyrazinamide, allocated at random. Both regimens were given for a total duration of either 6 or 4 months by random allocation. As previously reported, all 330 patients with drug-susceptible strains of tubercle bacilli pretreatment had a favorable bacteriologic response during chemotherapy, and only 2 (1%) of 158 in the 6-month series, compared with 15 (10%) of 156 in the 4-month series, relapsed bacteriologically during the 30 months after the start of chemotherapy. A long-term follow-up assessment has been conducted 5 to 8 yr after admission to the study. The excellent results in the 6-month series were maintained; only 1 of the 138 patients assessed relapsed after 30 months, compared with 5 of the 131 in the 4-month series. Of 33 patients with bacilli resistant to isoniazid, streptomycin, or both drugs pretreatment, 1 had an unfavorable response during treatment, and none of 9 in the 6-month series and 2 of 22 in the 4-month series relapsed bacteriologically by 30 months, but none of the nine 6-month and eighteen 4-month patients assessed relapsed subsequently.