The fundamental and clinical studies on cefotiam (CTM) were performed in the field of pediatrics, and the following results were obtained: 1. The peak MIC's of CTM against Gram negative rods such as E. coli, Klebsiella, Salmonella, Proteus were 1.56 mcg/ml. The MIC distribution against S. aureus was almost equal to the conventional cephalosporin antibiotics. The MICs against P. pseudomonas and Serratia were over 400 mcg/ml. 2. The mean serum levels of CTM after bolus intravenous injection of 25 mg/kg were 59.9 mcg/ml after 15 min., 30.0 mcg/ml after 30 min., 15.6 mcg/ml after 1 hour. 3. Administration of CTM to 6 pediatric patients produced the clinical responses which were good in all 6 cases and the bacterial effects of eradication in 3 cases and superinfection in the 2 cases in the 5 cases from whom the organism were isolated. No side effect was observed. From the above results, it is considered that a bolus injection of CTM 25 mg/kg t.i.d. to q.i.d. is a safe and useful treatment for pediatric cases.