From the experiments which have been reported, it follows that animals sensitized with one azoprotein react not only to the antigen used for the sensitization, but also to other azoproteins made up from the same simple azo-compounds and another protein. Although the specificity of the reaction has not yet been tested with various azo-components, its actual existence can reasonably be assumed on the basis of the phenomena observed in precipitation reactions. The sensitization is brought about with less facility than sensitization against the usual antigens and the effects are not uniform. Still, after sufficient treatment, 40 per cent of the animals succumbed with typical anaphylactic symptoms, mostly within a short time while 16 per cent showed severe symptoms.