An allergenic protein from Artemisia vulgaris pollen has been purified to homogeneity. Its molecular weight in native conditions is 47,000. The purified allergen, hereafter denominated Art v I, is a monomeric protein. It is a clinically relevant allergen since, at least, 70% of the individuals allergic to Artemisia vulgaris pollen have specific IgE in serum and in mast cells, demonstrated by ELISA and skin prick tests, respectively.