Pharmacokinetic, bacteriological and clinical studies on sultamicillin (SBTPC) fine granule were carried out in the field of pediatrics. The results obtained are summarized as follows. 1. Antibacterial activities of SBTPC against clinically isolated strains of Haemophilus influenzae, Haemophilus parainfluenzae, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Staphylococcus aureus, Branhamella catarrhalis, and Escherichia coli were compared with those of ampicillin (ABPC). SBTPC was superior to ABPC especially against beta-lactamase producing H. influenzae, E. coli, S. aureus, and B. catarrhalis. 2. Serum concentrations and urinary excretion rates of sulbactam (SBT) and ABPC after administration of SBTPC fine granule at a dose level of 10 mg/kg in 2 cases were determined. Mean half-lives of SBT and ABPC in the serum following oral administration were about 1.33 and 1.61 hours respectively. Mean urinary recovery rates of SBT and ABPC in 6 hours after oral administration at a dose of 10 mg/kg were 58.7% and 49.6% respectively. 3. SBTPC fine granule was administered to 20 pediatric patients with various bacterial infections (pneumonia 8 cases, bronchitis 2, pharyngitis 2, tonsillitis 4, subcutaneous abscess 1 and urinary tract infection 3). The overall clinical efficacy rate was 100% and the overall bacteriological eradication rate was 75%. 4. No adverse reactions were observed except 1 case of loose stool. No abnormal laboratory test values were observed. These results indicate the usefulness of SBTPC fine granule in the treatment of bacterial infections in children.