Enterobacter aerogenes, one of the most frequently isolated nosocomial pathogens in France, is exhibiting increasing multidrug resistance mechanisms associated with a change in membrane permeability. For drugs of the quinolone family, mutations in the target and active efflux play a prominent role in the resistance. We report here the effect of several pyridoquinoline derivatives that restore a noticeable fluoroquinolone accumulation to resistant strains that overexpress the MarA activator. Studies of the energy-dependent quinolone efflux indicate that the most efficient derivatives tested probably inhibit the resistance process by acting as substrate competitors on the pump extruding intracellular norfloxacin.