Pseudomonas aeruginosa is a frequently isolated bacterium in the veterinary practice, causing mainly dermatological, urinary, respiratory and systemic infections. The bacterium is frequently multiresistant and can develop resistance even during therapy, thereby the effective treatment of these infections frequently proves difficult. One possibility is to use synergistic combinations against these bacteria, involving aminoglycosides, fluoroquinolones, polymixins and antipseudomonal beta-lactams. In our studies the checkerboard microdilution method is utilized to describe interactions (addition, antagonism and synergy) between the investigated antibiotics. In addition, 8-day serial passages are conducted to investigate the possible resistance-delaying effect of certain combinations.