Fundamental and clinical studies have been performed on BRL 25000 (clavulanic acid 1 part-amoxicillin 2 parts) granules in the pediatric field. The antibacterial activities of BRL 25000 and amoxicillin (AMPC) were investigated against clinically isolated and laboratory stocked strains. BRL 25000 was superior to AMPC against strains of E. coli, Salmonella sp. and Klebsiella sp., and similar against Gram-positive cocci. Serum concentrations of AMPC and clavulanic acid (CVA) were measured 0.25, 0.5, 1, 2, 4 and 6 hours after administration of BRL 25000 granules at dose levels of 7.5, 10, 15 and 20 mg/kg. At 7.5 mg/kg peak level of AMPC of 2.69 micrograms/ml was achieved about 2 hours after dosing with a biological half-life of 1.64 hours; corresponding value for CVA was 0.53 micrograms/ml at 1 hour with a T 1/2 of 1.46 hours. At 10 mg/kg, AMPC also peaked after 2 hours (3.82 micrograms/ml) and the T 1/2 was 1.63 hours, whilst for CVA the value was 0.56 micrograms/ml with a T 1/2 of 1.24 hours. Value for AMPC at 15 mg/kg was 5.18 micrograms/ml at 1 hour post dose with a T 1/2 of 1.48 hours, and for CVA 4.01 micrograms/ml at 1 hour with a T 1/2 of 0.89 hour. At the highest dose of 20 mg/kg, AMPC level reached 4.21 micrograms/ml after 2 hours with a T 1/2 of 2.39 hours, and the CVA peak was 1.64 micrograms/ml at 1 hour with a T 1/2 of 1.01 hours. The 6 hours urinary recovery of AMPC and CVA following administration of the BRL 25000 granules ranged from 38-64% and 2-33%, respectively. In the clinical studies, the BRL 25000 granules are administered to 15 cases with pediatric infections and the clinical response was excellent or good in all cases treated (100%). Bacteriological investigation was performed on 13 strains from 12 cases and all strains were eradicated (100%). Regarding side effects, elevation of eosinophil was observed in 1 case and vomiting in 3 cases.