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. The experiments show that it is possible to make animals hypersensitive against a simple chemical group like para-arsanilic acid, and from this point of view connection would seem to be established with the phenomena of drug allergy in human beings. There is an essential difference, however, in that the sensitized animals did not react on injections of simple compounds such as para-amino-phenyl-arsanilic acid and phenyl-4-arsonic-acid-azo-tyrosine uncombined with protein. It remains to be determined whether under changed conditions positive results in this direction can be obtained. For this purpose it seems advisable to make experiments with isolated organs, according to the method of Schultz and Dale. While the simple substances failed to elicit direct reactions, they protected (as was foreseen by Doerr) against a subsequent injection of the active antigen. Similar compounds not containing the arsanilic acid group were considerably less active. The phenomenon is comparable to the inhibition of precipitin reactions already described. Considering the protection as a condition of antianaphylaxis, one would suppose that the simple substances mentioned are fixed by the cells in which the anaphylactic reaction takes place. It may be concluded that: 1. Animals can be sensitized through injections of one azoprotein-protein combined with diazotized para-arsanilic acid-against another compound containing the same azo-component but a different protein. 2. Injections of related simple compounds, as for instance para-arsanilic acid and phenyl-4-arsonic-acid-azo-tyrosine did not cause shock in the sensitized animals under the conditions of the present experiments. 3. The simple compounds mentioned and other related substances as well protect against the anaphylactic action of azoprotein, by inducing a state of antianaphylaxis.