Three hundred bacterial strains from positive urine cultures were isolated over a 10 months period in paediatric hospitalized and out-patients. In addition to commonly used antibiotics, each strain was tested for amoxycillin-clavulanic acid (Augmentin, Beecham) susceptibility. This antibiotic, which is a potent inhibitor of bacterial beta lactamases, may be of interest in the treatment of urinary tract infections because of its pharmacokinetics and activity. The antibacterial activity of amoxycillin and Augmentin against Enterobacteriaceae with special reference to Escherichia coli was compared. The resistance phenotype of Enterobacteriaceae to amoxycillin, carbenicillin and cephalothin allows to anticipate the nature of the beta-lactamase produced by a particular strain, and infer the activity of Augmentin. The overall activity of Augmentin should be interpreted taking into account the resistance phenotypes. In our study, Augmentin was active against 90% of E. coli strains, almost all Proteus mirabilis and vulgaris strains but 9 out of 24 Klebsiella strains were resistant. Augmentin had no activity against nosocomial Enterobacteriaceae, nor against Pseudomonas aeruginosa. On the other hand, its activity was of interest against penicillinase producing Staphylococcus. Our results confirm the interest of Augmentin as a preferential treatment of urinary tract infections in children.