The outcome of treatment for pulmonary tuberculosis using isoniazid and rifampin for 9 months supplemented by ethambutol for the initial 2 months was evaluated in a cohort of 233 patients. All patients had sputum cultures positive for Mycobacterium tuberculosis sensitive to isoniazid and rifampin. Of the 233 patients, 200 completed the regimen without change. Four patients had adverse reactions necessitating discontinuation and four became pregnant and had ethambutol substituted for rifampin. All eight were treated successfully with altered regimens. Ten patients were lost to follow-up, seven died, and eight were transferred to other jurisdictions. No patients failed to convert their sputum during therapy. At completion of therapy, three patients (1.5%) were found to have positive sputum. Follow-up 6 months after completion of treatment in 174 successfully treated patients revealed four (2.3%) with positive sputum. No further relapses were detected on evaluation 12 months after treatment was completed. All seven patients who failed therapy or relapsed were retreated successfully using the same regimen. These data provide a reference standard against which newer treatment regimens, such as the 6-month regimen currently in use, can be compared. In addition, the value of routine evaluations in detecting relapses at the time treatment is completed and 6 months later was substantiated, but 12-month follow-up was not useful.