Fundamental and clinical studies of cefixime (CFIX) granules, a new oral cephalosporin, were carried out with the following results: The MICs of CFIX against 234 clinical isolates were determined. Antibacterial activities of the drug against S. aureus, S. epidermidis and E. faecalis were weaker than those of conventional oral cephalosporins but antibacterial activities against Gram-negative bacteria were almost the same as those of cephem antibiotics of the Fujii's group 5. Peak serum concentrations of CFIX after oral doses of 3 and 6 mg/kg were, respectively, 1.51-4.86 micrograms/ml at 2-6 hours and 3.22-7.76 micrograms/ml at 4-8 hours. Serum concentrations of CFIX were dose-dependent in a patient given 3 and 6 mg/kg in a cross-over study. CFIX granules were administered mainly to children suffering from respiratory tract infection, otitis media and urinary tract infection at a dose of 3 mg/kg b.i.d. or t.i.d. for 3-27 days. The clinical responses to CFIX were excellent to good in 44 of the 50 children with infections, with an effectiveness rate of 88%. Thirty-five strains of the 40 clinical isolates were eradicated by the treatment with CFIX. The bacteriological eradication rate was 87.5%. Side effects observed were diarrhea and soft stool in 2 patients each, and elevated GOT X GPT and eosinophilia in 1 patient each. These symptoms and laboratory abnormalities disappeared on the day after the completion of therapy with CFIX. From the above results it has been concluded that CFIX is a useful and safe antibiotic for treating various bacterial infections in children.