A mathematical model for the release of peptide-binding drugs from affinity hydrogels is analyzed in detail. The model is not specific to any particular peptide/drug/gel system, and can describe drug release from a large class of affinity systems. In many cases, it is shown that the model can be reduced to a coupled pair of nonlinear partial differential equations for the total drug and peptide. Quantitative information relating the rate of drug release to the values of the model parameters is presented. Numerical solutions are displayed that illustrate the rich variety of release behaviors the system is capable of exhibiting. Theoretical release profiles generated by the model are compared with experimental release data from three different studies, and good agreement is found. The development of reliable mathematical models for affinity hydrogels will provide useful design tools for these systems.