The efficacy of ofloxacin, rifampicin and isoniazid was prospectively compared with the regimen of ethambutol, rifampicin and isoniazid for the primary treatment of pulmonary tuberculosis in 124 patients. All drugs were given orally daily for nine months. Culture conversion rates three months after starting treatment were 98 percent in the ofloxacin group and 94 percent in the ethambutol group; by six months all patients in both groups were culture-negative. Significant radiological improvement of pulmonary infiltrates was observed in 83 percent of the ofloxacin group and 85 percent of the ethambutol group one year after starting treatment. No relapse in either group was observed during a two-year follow-up period after the cessation of chemotherapy. Ofloxacin appears to be as useful as ethambutol in the treatment of pulmonary tuberculosis when either drug is combined with isoniazid and rifampicin.