Cefodizime (CDZM, THR-221), a new cephem antibiotic, was investigated for its clinical efficacy and pharmacokinetics in children. The results obtained are summarized as follows. 1. Antimicrobial activities Antimicrobial activities of CDZM against clinically isolated organisms were determined. MICs of CDZM against 1 strain each of Streptococcus pneumoniae, Escherichia coli and Klebsiella pneumoniae were 0.05 micrograms/ml to 0.10 micrograms/ml. Especially, MIC against all 6 strains of Haemophilus influenzae was less than or equal to 0.024 micrograms/ml. This MIC value was lower than those of other antibiotics such as cefotaxime, cefotiam, cefazolin, piperacillin. 2. Pharmacokinetics CDZM was given to 1 case at a dose of 20 mg/kg by a 60-minute intravenous drip infusion. The peak value of serum concentration of CDZM was 207.80 micrograms/ml at the end of the infusion. The half-life was 2.15 hours. The mean urinary excretion rate was 68.5% in the first 4 hours, 79.2% in 6 hours and 76.5% in 8 hours after the 30-minute drip infusion. 3. Clinical efficacy CDZM was given to a total of 27 patients, 13 with pneumonia, 1 with bronchitis, 2 with acute pharyngitis, 1 with purulent tonsillitis, 5 with urinary tract infection, 1 each with retrograde cholangitis, acute enteritis, pericementitis, phlegmon and inguinal lymphadenitis. Overall clinical efficacies were excellent in 5 cases, good in 17 and the efficacy rate was 81%. Bacteriological effects were investigated in 13 cases and the eradication rate was 85%. No adverse reactions were observed in any case. As abnormal laboratory findings, elevated GOT, GPT, A1-P, LAP and gamma-GTP, were noted in 1 out of the 28 cases examined.