Development of antibiotic resistance in bacteria is a problem of great concern. It is important to establish the convenience of antimicrobial susceptibility tests in animal infections. The aim of this study was to test the susceptibility to antibiotics of Pseudomonas strains isolated from chronic canine otitis externa. We tested 23 strains of Pseudomonas: 19 Ps. aeruginosa, three Ps. fluorescens and one Pseudomonas spp. The most effective antibiotics were tobramycin (100 % susceptible), marbofloxacin (91.3 %) and ceftazidime (91.3 %). Ticarcillin and gentamicin, commonly used for the treatment of otitis externa also showed good results (susceptibility of strains was 86 and 65.2 % respectively). Lower susceptibility was found using enrofloxacin (52.1 %) probably due to its indiscriminate use. We emphasize the need for a rational policy of antibiotic prescribing in order to prevent the selection of resistant strains.