The present invention relates to a process for the controlled enzymatic cleavage of purified and depigmented active allergenic proteins from indoor and outdoor source materials, which process produces fragments of allergens that retain the the natural T-lymphocyte stimulating epitopes, but are depleted of IgE-binding B-cell epitopes and complement-activating agents. The invention also relates to the new pharmaceutical products. These allergen fragments do not exhibit the disadvantages of conventional allergenic extracts for immunotherapy and can be safely used to induce a state of specific T-cell anergy and immunological tolerance in allergic human beings.