1. Antisera to R-salt-azo-benzidine-azo-crystalline egg albumin give precipitates with crystalline egg albumin by virtue of their antidye content.
2. The quantitative course of the reactions with increasing amounts of antigen is very similar for the dye-antidye and egg albumin-anti-egg albumin systems, but differs markedly for the cross reaction between egg albumin and antidye.
3. A possible explanation for the occurrence of this one-sided crossreaction is given in terms of reactive groupings on the antigen and antibody.
4. A qualitative expression of the course of the cross-reaction is given in terms of the laws of classical chemistry.