Methods for producing an allergen composition, methods for in vitro diagnosis of type I allergy, and diagnostic kits for performing diagnosis employ Bos d 23k allergen of SEQ ID NO: 4, or the mature protein thereof, or a variant or fragment of the Bos d 23k allergen or the mature protein sharing epitopes for antibodies with the Bos d 23k allergen or the mature protein. Methods for treatment of a Type I allergy to a mammal and pharmaceutical compositions employ a Bos d 23k allergen of SEQ ID NO: 4, or the mature protein thereof, or a variant or fragment of the Bos d 23k allergen or the mature protein sharing epitopes for antibodies with the Bos d 23k allergen or the mature protein, wherein the Bos d 23k allergen, the mature protein, the variant or the fragment is modified to abrogate or attenuate its IgE binding response.
