I. Pharmacokinetics (1) CXM 24.4 and 31.9 mg/kg were administered by intravenous drip infusion for 4 hours. The plateau levels were obtained at 1 approximately 2 hours, the blood levels at which time were 25.6 and 33.8 micrograms/ml respectively with dose response observed. (2) The respective half-lives were as short as 49.4 and 36.2 minutes. (3) The total clearances were 74.6 and 127.2 ml/min respectively; when calculated on plateau level and infusion rate, these were 81.6 and 111.0 ml/min. These differently determined values were near each other. (4) The respective renal clearances were 157.8 and 101.9 ml/min. II. Clinical results CXM for intravenous use was administered to 21 pediatric patients, and the clinical results were good and excellent in 19 (90.5%). Excluding 2 cases with elevation of cold hemagglutination values, the efficacy rate of 94.7% (18/19 cases) was achieved. The doses administered ranged 44 approximately 100 mg/kg body weight, and this dosage level was considered enough to achieve clinical effect. With the current clinical trial we considered that although the effectiveness of this drug was proved in 3 approximately 7 day intravenous drip infusion and intravenous injection, the continued treatment with other oral antibiotic following CXM treatment would be necessary from the patients' general conditions and laboratory examination findings. No noteworthy side effects were observed in any of the patients. No abnormality was seen in biochemistry and electrolyte findings, either.