Background: At present, data about the cross-reactivity of Blomia spp. comes from studies made among different genera of mites, and no results have been published involving different species of the genus Blomia.

Objective: The aim of this study was to find out the level of cross-reactivity between the two main species of Blomia causing allergy, and its implication in the diagnosis of Blomia sensitization.

Methods: Using extracts from optimal growth phases of Blomia kulagini (Zakhvatkin, 1936) and Blomia tropicalis (van Bronswijk, Cock and Oshima, 1973) as allergenic material, the allergenic cross-reactivity between both house dust mites was evaluated by means of cutaneous tests, specific IgE values, ImmunoCAP-inhibition and SDS-PAGE- IgE-immunoblotting-inhibition.

Results: The results demonstrated that IgE-binding components belonging to both species are very similar from the immunological point of view, showing high correlations between both species when using cutaneous tests (R2=0.915) or specific IgE (R2=0.980). ImmunoCAP-inhibition and SDS-PAGE-IgE-Immunoblotting-inhibition probed with human sera, showed a total inhibition of specific IgE reactions by the heterologous antigens.

Conclusion: The results obtained strongly suggest the great resemblance between the allergenic composition of both species.

Key words: Blomia tropicalis, Blomia kulagini, mite allergens, cross-reactivity.