Bacterial infection (pyoderma) of the canine skin is largely caused by Staphylococcus intermedius and may be a superficial or deep infection. Pyoderma may be a primary, idiopathic disease or secondary to a range of other dermatological disorders. In this study, the serum concentrations of IgG, IgA, antistaphylococcal IgG and antistaphylococcal IgA were measured by ELISA in normal dogs (n = 22), dogs with idiopathic deep pyoderma (n = 22), atopic dermatitis and superficial pyoderma (n = 24), atopic dermatitis without pyoderma (n = 25), flea bite dermatitis with superficial pyoderma (n = 8), pustular demodicosis (n = 8) and German shepherd dogs with anal furunculosis (n = 28). The serum IgG was significantly increased in dogs with atopy and superficial pyoderma (p < 0.001), and lower than normal in dogs with idiopathic deep pyoderma (p < 0.015). The concentration of serum IgA was significantly lower than normal in dogs with atopy uncomplicated by pyoderma (p < 0.015). The concentration of antistaphylococcal IgG in all clinical sera was significantly elevated (p < 0.001) when compared to normal dogs but concentrations of antistaphylococcal IgA were no greater than in normal dogs. Western blotting analysis for determination of the specificity of serum IgG antistaphylococcal antibody revealed that there were nine major epitopes. Discriminant analysis demonstrated that particular combinations of these epitopes were recognised more frequently by sera from dogs in different clinical groups.