The in vitro proliferative responses of peripheral blood mononuclear cells from seven healthy basset hounds exposed to Malassezia pachydermatis antigen (500 μg/ml) exceeded (P<0.05) those of seborrhoeic basset hounds with high populations of M pachydermatis and eight Irish setters with glutensensitive enteropathy. The stimulation indices in the latter two groups and in eight healthy beagles were comparable. The stimulation indices of the four groups after exposure to phytohaemaglutinin did not differ significantly. The serum titres of M pachydermatis-specific IgG and IgA measured by enzymelinked immunosorbent assays (ELISA) in 21 seborrhoeic basset hounds and 11 affected dogs of various breeds exceeded those of 14 healthy basset hounds and eight healthy beagles (P<0.01 for IgG, P<0.05 for IgA). Total serum IgA concentrations measured by ELISA in the affected dogs were not lower than those of healthy dogs.