We developed the first models for predicting whether sites of protein modifications are inside or outside of protein-protein interacting regions (PPIRs), based on the existing structural and PTM databases. Our models show high predictive performance measures. As more data become available, the performance of these models should be even better. Specifically, discovery of new PPIRs as a result of rapidly increasing 3D structure determinations should increase the accuracy of the predictive models. These predictive models are available online and may be useful in providing additional insight related to the functional relationship between specific PTMs and protein-protein interactions.