Extract from house dust mite (Dermatophagoides farinae) was treated with glutaraldehyde (GA) and examined for its allergenicity and immunogenicity. The allergenicity of glutaraldehyde-treated mite extract (GA-M) was decreased significantly when compared with untreated mite extract (UN-M) by skin test in mite allergic individuals. Immunogenicity of GA-M was at least similar with that of UN-M, when examined by formation of antibodies to UN-M in guinea pigs. Fractionations of GA-M and UN-M revealed that polymerization occurred and proteins of higher molecular weight increased after the treatment of mite extract with GA. The results suggest potential usefulness of the polymerized mite antigens in immunotherapy.