Serum immunoglobulin G (IgG) responses of healthy dogs and dogs with Malassezia pachydermatis dermatitis were compared by Western immunoblotting. M pachydermatis CBS 1879 was disrupted mechanically and its proteins were separated and blotted on to nitrocellulose membranes before being incubated with sera from eight healthy beagles, eight Irish setters with gluten.sensitive enteropathy, 15 healthy basset hounds, and 30 dogs with M pachydermatis.associated dermatitis, 20 of which were basset hounds. The mean (se) numbers of bands of immunoreactivity observed in the seborrhoeic basset hounds (10.7 [0.41) and affected mixed.breed dogs (9.4 [0.9]) were significantly greater than in the beagles (3.0 [1.0]), Irish setters (5.5 [1.1]) and healthy basset hounds (5.6 [0.7]). The number of bands identified was correlated (rs=0.76, P<0.001) with the anti-M pachydermatis IgG values measured by ELISA in a previous study. Most of the dogs were immunoreactive towards the 132, 66 and 50 to 54 kDa proteins and the affected dogs were also usually reactive towards the 219, 110, 71 and 42 kDa proteins.