In a study in Singapore, patients of Chinese, Malay, and Indian ethnic origin with sputum-smear-positive pulmonary tuberculosis were allocated at random to daily treatment with streptomycin, isoniazid, rifampin, and pyrazinamide for 2 months (2SHRZ), for 1 month (1SHRZ), or for 2 months without streptomycin (2HRZ), followed, for all patients, by 3-times-weekly isoniazid and rifampin (H3 R3) up to 6 months. As previously reported, all except 1 of 319 patients with drug-susceptible tubercle bacilli pretreatment had a favorable bacteriologic status at the end of chemotherapy, and among the 300 patients assessed up to 30 months (24 months after the end of chemotherapy), there was only 1 bacteriologic relapse in each series, giving an overall therapeutic failure rate of only 1.3%. Follow-up has been continued at 6-month intervals up to 5 yr. During the 5 yr, the total relapse rate for patients with drug-susceptible strains pretreatment was 2.4% of 297 patients (95% confidence limits, 1.0 to 4.8%). Among the 31 patients with strains resistant to isoniazid, streptomycin, or both drugs pretreatment, there were no failures during chemotherapy and 4 (13%) subsequent relapses.