Abstract: When rabbits were immunized with a mixture of purified streptomycin and dihydrostreptomycin and Freund's complete adjuvant, anti-streptomycin and anti-dihydrostreptomycin antibodies were detected by indirect hemagglutination reaction.In our study of the antibody specificities, hemagglutination inhibition tests with sera from rabbits immunized with streptomycin and dihydrostreptomycin were carried out. Streptomycin, dihydrostreptomycin, bis-(α-hydroxy-streptomycyl)-amine and the degradation products of streptomycin such as streptidine, streptobiosamine, maltol, streptomycinic acid and streptomycyl oxime were used as inhibitors. Their minimum concentrations required to inhibit hemagglutination were compared; among them bis-(α-hydroxystreptomycyl)-amine was found to be the strongest inhibitor, since its chemical structure is similar to the antigenic determinant of streptmycin allergen.The antigenic determinant of streptomycin allergy is the aldehyde group of streptomycin bound covalently with the amino group of protein.The dihydrostreptomycin antiserum has two kinds of antibodies, one is streptomycin antibody. The other antibody may be produced when guanidin group of dihydrostreptomycin binds to protein, polypeptide or nucleic acid to form dihydrostreptomycin antigen.