Fundamental and clinical evaluation of ceftazidime (CAZ) were carried out in neonates and premature infants, and the results obtained are summarized below. Serum concentrations of CAZ after administration of 20 mg/kg were satisfactorily high regardless of the route of administration; bolus intravenous injection or 1-hour intravenous drip infusion. Like other cephem antibiotics, half-lives tended to be shorter as day-ages of subject became higher. Although there were some differences in urinary recovery rates between different dosage groups, they were generally high. Clinical efficacy was either excellent or good in all 21 assessable cases. In 23 cases examined for adverse effects, diarrhea was observed in 1 case, and elevation of GOT and GPT, in another case.