Cefotaxime (CTX) was used for 129 cases in respiratory tract and other infections; 57 cases of pneumonia, 20 cases of bronchopneumonia, 20 cases of acute bronchitis, 14 cases of chronic bronchitis, 7 cases of acute exacerbation of bronchiectasia or pulmonary emphysema, 4 cases of suppurative diseases of the lung, 1 case of pyothorax, 1 case of retropharyngeal abscess, 3 cases of pleurisy and 1 case of urinary tract infection. (A case was excepted on clinical evaluation.) CTX was administered by intravenous injection or drip infusion at a daily dose ranging from 0.5 to 8 g, for a term of 2 to 61 days. The total dose patients received ranged from 3 to 226 g. The results obtained were as follows. Clinical effects; excellent in 45 cases, good in 63 cases, fair in 9 cases, poor in 7 cases and unevaluable in 4 cases. The efficacy rate was 87.1% (108/124). Bacteriological effects; eliminated in 30 cases, decreased in 8 cases, unchanged in 2 cases and replaced in 1 case. The elimination rate was 75.6% (31/41). Side effects and abnormal laboratory findings; general itching, fatigue in lower extremities and albuminuria in 1 case each, and anemia in 2 cases. Increased number of eosinophiles and elevated GOT in 1 case each, elevated GOT and GPT in 3 cases and elevated GOT, GPT and A1-P in 2 cases. These symptoms or abnormal laboratory findings disappeared after the discontinuation or termination of CTX therapy. In view of the above, CTX may be considered to be a clinically useful antibiotic against respiratory tract infections.