The study was undertaken in patients with newly diagnosed bacteriologically positive pulmonary tuberculosis. The patients were randomly allocated to receive one of two regimens. In one of the regimens, patients received 2 months of daily treatment with streptomycin, isoniazid, rifampin, and pyrazinamide (SHRZ) followed by isoniazid plus rifampin for 4 months (4 HR). In the other regimen, patients received 2 months of daily streptomycin, isoniazid, pyrazinamide, and ciprofloxacin (SHZ Cipro) followed by isoniazid plus ciprofloxacin for 4 months. All patients in the SHRZ/HR regimens and all but one in the SHZ Cipro/H Cipro regimens had a favorable bacteriologic response during chemotherapy. In the patients in the SHZ Cipro/H Cipro regimen, ciprofloxacin was well tolerated during the period of treatment. After chemotherapy, one (5.9 percent) of 17 patients in the SHRZ/HR group and three (16.6 percent) of 18 patients in the SHZ Cipro/H Cipro group relapsed bacteriologically.