Cefepime was the most active compound on the Enterobacteriaceae with a MIC90 of 0.26 microgram/ml and a resistance rate of 0.1%. Ceftazidime was the most active drug on the non-fermenting bacilli (MIC90 9.65 micrograms/ml; resistance rate 3%). Amikacin- and gentamicin-resistant strains showed a decreased susceptibility to the beta-lactams, though the Enterobacteriaceae and the non-fermenters remained fairly sensitive to cefepime and ceftazidime, respectively. Aminoglycoside-3-N-acetyltransferase was the most prevalent enzyme and was often associated with intermediate resistance or resistance to beta-lactams. Non-fermenters showing aminoglycoside impermeability were very often intermediately resistant or resistant to beta-lactams