Therapeutic effects of lividomycin (LVDM) were studied in 33 patients with respiratory infections including pneumonia, lung abscess, chronic bronchitis, etc. LVDM was intramuscularly administered at the dose of 1 or 2 g per day for consecutive 4 to 25 days. The results obtained are summarized below: 1. At the end of the first week of the treatment, rate of improvement in such parameters as cough, sputum, rales, fever and blood sedimentation rate were 69%, 56.7%, 60%, 79.2% and 70% respectively. Also, in 16% of the patients, abnormal shadow noted in X-ray film of the chest was disappeared and in 20% of the patients, size of the same was reduced during the first week of treatment. 2. Therapeutic effects of LVDM were evaluated synthetically and were graded as excellent, good, fair and ineffective. LVDM was effective in about 70 per cent of the patients, that is, excellent results were obtained in 4 patients, good in 12 patients, fair in 6 patients, and in 10 patients this antibiotic was ineffective. 3. In one patient with slight loss of high frequency perception was observed on the audiogram, but no other ototoxic effects such as subjective hearing loss, tinnitus, etc. In addition, no untoward effects on renal and hepatic function were observed. 4. The MIC values of LVDM for clinically isolated 20 strains of Pseudomonas aeruginosa were examined, using kanamycin for comparison. The MIC values of LVDM for many strains were superior to those of kanamycin. In view of the test results mentioned above, LVDM would appear to be useful medication for the treatment of some of respiratory infections.