Abstract: Certain isolated fractions, extracted from allergy-causing molds, have been found to be antigenic but non-allergenic, and are able to decrease substantially or prevent the susceptibility to mold allergens of allergic individuals. The antigenic non-allergenic fractions contain protein and carbohydrate and have molecular weights which have been found to vary with the mold source. Increased polyvalent protection can be realized by combining fractions from different molds, e.g. Alternaria with Hormodendrum or Helminthosporium. The extracts are administered parenterally, preferably subcutaneously in isotonic saline.