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