The efficacy, safety and pharmacokinetics of cefozopran (CZOP) were evaluated in neonates and the following results were obtained: 1. Of the 12 patients treated with CZOP, judgment of clinical efficacy was evaluable in 10 patients (including 5 with pneumonia and 3 with urinary tract infections). The treatment was effective and the causative organism was eradicated in 100% of the patients. 2. No adverse signs and symptoms were recognized during the treatment with CZOP. A slight elevation of direct bilirubin was recognized as an abnormal alteration of laboratory test values in one patient. The value, however, returned to the normal range after the completion of treatment. 3. The pharmacokinetic evaluation was made in 3 of the 12 patients. The blood CZOP levels were recognized in proportion with the dosages. The elimination half lives (T 1/2) in those patients were 8.92, 2.90 and 2.76 hours. Prolongation of T 1/2 was recognized in the patient aged 0 day. It was possible to examine the urinary excretion only in one patient aged 18 days. The excretion rate of the drug was 68.6% of dose by 8 hours after administration. These results suggest that CZOP is a drug useful for treatment of infections in neonates as well, with high efficacy and safety.