SummaryThe antigenic composition ofD. pteronyssinusextract was investigated by using antisera raised in rabbits by injection of the mile extract in Freund's adjuvant. Immunodiffusion analysis revealed the presence in the mite extract of many antigenic constituents, most of which were also common to human dander and house dust extracts. Four antigenic components not shared by human dander appeared to be common toD.farinaeextract.D. pteronyssinusextract was then fractionated on Sephadex G‐75 and DEAE‐Sephadex. Immunodiffusion analysis of the most active fraction revealed, after heat‐treatment, the presence of three precipitin lines, one of which appeared not to be shared by nutrient medium or byD. farinaeextract constituents.When the anti‐mite rabbit serum was fixed to an immunosorbent and incubated with a house dust extract it was constantly able to induce a strong decrease or a complete loss of the allergenicity of the dust extract in man. These results suggest that mite allergen(s) are immunogenic in the rabbit and provide more direct evidence for identity of the allergens in house dust a