Ofloxacin, a synthetic antibacterial pyridone-carboxylic acid derivative, was used in the treatment of intractable pulmonary tuberculosis. In this study, the therapeutic effect of Ofloxacin on pulmonary tuberculosis and Ofloxacin resistance were analyzed. All patients had been hospitalized in eight national sanatoria in Kinki district, and were excreting tubercle bacilli resistant to various anti-tuberculosis drugs agents. Ofloxacin was given to 118 patients orally at a daily dose of 300 mg to 600 mg for more than 3 months. A few anti-tuberculosis drugs, which had failed in the negative conversion of bacilli previously, were used in combination. By Ofloxacin, 23 patients (19.5%) showed negative conversion of tubercle bacilli in sputum culture within 5 months, and they remained culture-negative for at least 6 months after conversion. Side-effects were observed in 2 patients. One complained of arthralgia and the other felt abdominal fullness. But both were not serious. From these results, it was concluded that Ofloxacin was effective for intractable pulmonary tuberculosis. The resistance of tubercle bacilli to Ofloxacin increased significantly after it was used.