Regression analysis and substituent constants have been employed to analyze the roles of different intermolecular forces in hapten-antibody interaction using the experimental data of Pressman, Pauling, and their associates. From a study of benzoate and arsonate haptens with various antibodies, it was concluded that steric repulsion by substituents, as measured by the Es parameter, is the most important variable. Hydrophobic and electronic effects of substituents appear to be much less important. © 1969.