During 8 months from October 1986 to May 1987, the clinical efficacy of sulbactam/ampicillin (SBT/ABPC) was evaluated in 63 pediatric inpatients with various infections. Clinical efficacies were evaluable in 58 patients among them (consisting of 2 patients with sepsis, 3 with tonsillitis, 12 with bronchitis, 6 with bronchopneumonia, 24 with pneumonia, 1 with phlegmon, 2 with lymphadenitis, 1 with impetigo and 7 with urinary tract infection) and were excellent in 40 patients and good in 17 with an overall efficacy rate of 98.3%. Bacteriological efficacies were assessed in 25 patients and 27 strains of organisms (consisting of 3 strains of Staphylococcus aureus, 2 Streptococcus pneumoniae, 1 Streptococcus pyogenes, 2 beta-Streptococcus, 1 Gram-positive cocci, 5 Escherichia coli, 1 Enterobacter aerogenes, 7 Haemophilus influenzae, 2 Haemophilus parainfluenzae, 1 Branhamella catarrhalis, 1 Proteus mirabilis and 1 Salmonella subgenus I). Bacteriological eradication rates were 88.9% for Gram-positive organisms, 66.7% for Gram-negative organisms and 74.1% overall. No superinfection was observed in any of patients treated. Side effects and clinical laboratory parameter abnormalities observed consisted of diarrhea in 7 (11.1%) of the 63 patients, eosinophilia in 2 (3.3%) of 61 tested, thrombocytosis in 3 (5.5%) of 55, elevation of direct bilirubin in 1 (3.3%) of 30, elevation of total bilirubin in 1 (3.1%) of 32, elevation of GOT in 4 (6.8%) of 59 and elevation of GPT in 1 (1.7%) of 59 patients tested. As an effect on the hemostatic mechanism of this drug, PIVKA II was detected in 1 patient (4.2%) of 24 tested, but findings of other coagulation tests were normal and none of patients showed bleeding tendency or inhibition of platelet aggregation. From the above results, it appears that SBT/ABPC is an efficacious and safe drug in the treatment of bacterial infections of pediatric patients.