Abstract: Chemically modified allergens, whose allergenic activity is reduced with respect to that of the corresponding native allergenic material, which are capable of inducing specific antibodies addressed towards said native allergenic material, wherein a portion of the primary amino groups of the protein molecule of the native allergen are chemically modified so as to give simple or substituted carbamylic amino groups, or substituted thiocarbamylic amino groups, or possibly substituted guanidino groups, and process for the production thereof. The allergens so modified are not polymerized with each other, they are soluble in water media, they are resistent to tryptic hydrolysis and they show particularly suitable for being administered in hyposensitizing therapeutic treatments.