Epidemiologic and in vitro data have shown that the association of housedust mite (HDM) allergy and snail allergy in the same patients was due to cross-reactivity between HDM and snail allergenic components. However, the cross-reacting allergen(s) have not yet been identified. In vitro reactivity of seven patients' sera to the various extracts and hemolymph of four different Helix snail species was analyzed by IgE detection on immunodots and Western blots. Cross-reactivity between snails and Dermatophagoides pteronyssinus was assessed by immunodot and ELISA inhibition in two patients. Heterologous inhibition of the snail immunodot and ELISA was observed in one serum. Western blotting showed a specific binding on all four snail species extracts: molecular weights of snail allergens ranged from <21 to 200 kDa. Marked individual differences were observed in the seven sera under study: most sera demonstrated IgE recognition of multiple bands, illustrating that no single allergen is responsible for cross-reactivity between snail and mite. These results confirm that cross-reactivity exists between snails of the Helix genus and HDM. This cross-reactivity, involving more than a single allergen, may be of clinical significance in atopic patients allergic to D. pteronyssinus. The identity of the cross-reacting allergens remains to be determined. Potential candidates include the thermostable minor allergens of D. pteronyssinus, tropomyosin and hemocyanin. Diseases, Environment.