The significance of reactions to crude extracts and purified fractions of the house dust mites Dermatophagoides pteronyssinus (Der p I and Der p II) and Dermatophagoides farinae (Der f I and Der f II) was evaluated in dogs with clinical manifestations of atopic dermatitis (AD). In 13 healthy control dogs and eight dogs with AD, immediate skin test reactivity was determined to serial dilutions of Der p I, Der p II, Der f I and Der f II. In addition, allergen-specific IgGd antibodies were determined by means of an enzyme-linked immunosorbent assay (ELISA) and Western blots. The results suggest that, in contrast to what occurs in humans and despite immediate skin test reactivity in some dogs, Der p I, Der p II, Der f I and Der f II are unlikely to be major allergens in dogs with AD. However, only serum of atopic dogs consistently binds a 90 kDa polypeptide of D. farinae, as shown by Western blot analysis.