Fundamental and clinical studies on cefuzonam (CZON, L-105) were carried out and the results obtained are summarized below: MICs against 451 clinical isolates of Staphylococcus aureus were determined. Antibacterial activity of CZON on S. aureus was similar to that of cefazolin, inferior to that of cloxacillin, and superior to those of benzylpenicillin and cefotaxime. With one-shot intravenous injection of CZON, peak serum concentrations were 40.0 micrograms/ml and 97.5-145 micrograms/ml with a dose of 10 mg/kg and 20 mg/kg, respectively. Half-lives of the drug in serum were 34.2-47.9 minutes. Urinary excretion rates were 46.8-67.3% in 4 hours after injection. In all of 13 cases of pediatric infections tested, the clinical efficacy was excellent or good. Side effects observed were diarrhea in 4 patients, and elevated GOT and thrombocytosis in 1 patient each. From the above results, we have concluded that CZON is useful and safe antibiotic for treating various bacterial infections in children.