Eighty-three dogs with clinical signs of otitis externa and with ear cytology revealing microbial organisms were studied. Samples were collected from both ears of each dog by inserting two swabs successively into each ear canal, rotating each once through 360° and then rolling it out in a line on to a glass slide. For each animal, four single parallel smears (SPS) were made on one slide, which was then appropriately labelled to identify the animal as well as the order of the samples. The slides, one representing each animal, were subsequently stained with modified Wright's stain. Six high-power fields of every SPS were counted. Golden retrievers and West Highland white terriers were found to be predisposed to developing otitis externa (P=0.0006 and P=0.0123, respectively). Otitis externa occurred significantly more frequently in dogs with pendulous pinnae than in dogs with erect pinnae (P=0.0009). There was no significant difference between the first and the second samples with respect to the number of microorganisms found (P>0.1 for cocci and P>0.5 for rods and yeasts), and there was a substantial agreement between the results of the two successive swabs for the presence of cocci (κ=0.765) and rods (κ=0.705). For yeasts, the agreement was only moderate (κ=0.581).