This study evaluated the in vitro effects of the combination of a carbapenem (imipenem or meropenem) with a quinolone (ciprofloxacin or levofloxacin) using a microbroth dilution chequerboard technique and multidrug-resistant Pseudomonas aeruginosa strains. The ciprofloxacin and meropenem combination was only synergistic against 2 strains (6.2%) and ciprofloxacin and imipenem against 1 strain (3.1%). Levofloxacin and imipenem or meropenem were not synergistic for against any strain. None of the combinations showed an antagonistic effect.