The usefulness of sulbactam/ampicillin (SBT/ABPC) in the treatment of pediatric infections was evaluated. 1. Twenty pediatric patients with infection were treated with SBT/ABPC and an intravenous dosage of 27.8-47.4 mg/kg, 3 to 4 times a day. Clinical efficacies in 18 patients excluding 2 patients of Mycoplasma pneumonia (9 cases of pneumonia, 6 urinary tract infection, 1 tonsillitis, 1 maxillary sinusitis and 1 osteomyelitis) were judged to be excellent in 13 patients and good in 5. There was no case of failure. 2. Bacteriological efficacies against 16 strains (1 Staphylococcus aureus, 3 Enterococcus faecalis, 4 Haemophilus influenzae, 2 Haemophilus parainfluenzae, 5 Escherichia coli and 1 Serratia sp.) isolated from 13 of the 18 patients were rated as "eradicated" for 13 strains, "decreased" for 1 and "unchanged" for 2 with an eradication rate of 81.3%. Of 13 strains eradicated, 3 were those with high beta-lactamase productivity. 3. Rash as a side effect developed in 1 patient and eosinophilia and elevated GOT and GPT were observed in 7 patients but none of them were serious. 4. Blood levels of the drug following an intravenous dose of 30 mg/kg were determined in 2 pediatric patients. Blood levels of SBT and ABPC at 30 minutes after intravenous administration were 19.0 and 29.2 micrograms/ml in one patient and 21.0 and 31.6 micrograms/ml in another, respectively, and those at 4 hours were 0.48 and 0.62 microgram/ml in one patient and 0.59 and 0.89 microgram/ml in another, respectively. The half-lives of SBT were 0.67 and 0.70 hour and those of ABPC were 0.64 and 0.69 hour in the 2 patients, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)