Basic and clinical studies were made on cefmenoxime (CMX) in pediatric field, and the following results were obtained. 1. The antibacterial activity of CMX against clinically isolated and maintained strains was examined. CMX had stronger antibacterial activity than CEZ against Escherichia coli, Salmonella, Klebsiella pneumoniae, Proteus mirabilis, Serratia marcescens and Pseudomonas aeruginosa, but CEZ had stronger antibacterial activity against Staphylococcus aureus. 2. The blood concentrations of CMX, 0.5, 1, 2, 4 and 6 hours after a one-shot intravenous injection of 20 mg/kg of CMX were 33.6, 15.1, 4.5, 2.5 and 0.6 mcg/ml, respectively, with the half-life of 1.04 hours. 3. The blood concentrations of CMX, 0.5, 1, 2, 4 and 6 hours after a 1-hour intravenous drip infusion of 20 mg/kg of CMX were 32.0, 55.2, 8.4, 4.2 and 1.0 mcg/ml, respectively, with the half-lite of 0.96 hour. 4. A complete or partial clinical response to therapy with CMX was obtained in all 10 children with infectious diseases. 5. Bacteriological examination made on 3 patients showed that all bacteria had been eradicated, and that therapy was effective. The bacteria were E. coli in 2 patients and Proteus mirabilis in 1 patient. 6. The side effects produced were neutropenia, eosinophilia and skin eruption in 1 patient, and diarrhea in 1 patient.