The aim of this study was to compare in vitro activity, measuring minimal inhibitory concentration, of amoxicillin or its combination with clavulanic acid against 109 strains of Acinetobacter baumanii, 104 strains of Hemophilus influenzae and 94 strains of Staphylococcus aureus. All these were obtained from different hospitals of the Santiago Metropolitan Region. Amoxicillin-clavulanic acid association did not improve the activity of amoxicillin against Acinetobacter. The association was not active against methicillin resistant strains of S aureus; instead, it significantly increased the activity of amoxicillin against methicillin susceptible strains. All the H influenzae strains were susceptible to the combination.