BRL 25000 is a preparation comprising 2 parts of amoxicillin (AMPC) to 1 part of clavulanic acid (CVA). Basic and clinical studies have been performed on BRL 25000 granules in the pediatric field. The antibacterial activities of BRL 25000 and AMPC against 48 strains of E. coli isolated from patients with urinary tract infections were studied. The MICs of BRL 25000 were all below 100 micrograms/ml, except for 1 strain with MIC greater than or equal to 800 micrograms/ml. However, 19 strains (40%) were resistant to AMPC, with MICs more than 800 micrograms/ml. BRL 25000 granules were administered to 23 children with bacterial infections and the clinical response was assessed as excellent in 10, good in 9, fair in 3, poor in 1, giving an overall efficacy rate of 83% (19/23). Isolated organisms were eradicated in 12 out of the 16 strains which were evaluated bacteriologically. Changes in intestinal bacterial flora following administration of BRL 25000 granules were studied in several children and decreases in flora were observed in some cases. No severe side effects were observed although three seemed to be a slightly higher incidence of diarrhea than with other drugs.