Laboratory and clinical studies of sulbactam/ampicillin (SBT/ABPC) in children have been carried out, and the following results were obtained. 1. Antibacterial effect MICs of SBT/ABPC were only one-tube less than or similar to those of ABPC against susceptible organisms. Against ABPC-resistant organisms at the inoculum size of 10(8) cells/ml however, SBT/ABPC was superior to ABPC when evaluated in terms of their MIC values. When MICs of SBT/ABPC were compared to those of ABPC against organisms with high beta-lactamase producing activities, it was found that many of ABPC-resistant organisms were much susceptible to SBT/ABPC. 2. Absorption and urinary excretion In 2 cases to which 50 mg/kg and 20 mg/kg SBT/ABPC were respectively given over 30 minutes by drip infusion, peak serum levels were obtained at the end of the drip infusion with peak levels of SBT of 45.5 micrograms/ml, 12.5 micrograms/ml, respectively and those of ABPC of 83.0 micrograms/ml, 22.9 micrograms/ml, respectively. The half-lives of SBT and ABPC were 0.94 hour and 0.98 hour, respectively. The mean urinary excretion rates in the first 6 hours after the end of administration were 84.4% for SBT and 63.1% for ABPC. 3. Clinical results Clinical efficacies were evaluated in 24 cases including 9 cases of pneumonia, 2 cases of upper respiratory infection, 7 cases of urinary tract infection and 1 case each of bronchopneumonia, pyothorax, tonsillitis, streptococcal infection, ++ phlegmon and staphylococcal scalded skin syndrome. Clinical efficacies were excellent or good in 19 cases with an overall efficacy rate of 86.4%. Adverse effect was found in 1 case with nausea and vomiting, and abnormal laboratory test values observed were 2 cases each of eosinophilia, slight elevation of GOT and GPT and elevation of LDH, but they were not serious.