This document provides methods and materials involved in assessing responsiveness to PARP inhibitors and platinating agents. For example, methods and materials for using levels of non-homologous end-joining pathway members (e.g., artemis mRNA or polypeptide levels, Ku80 mRNA or polypeptide levels, or DNA-PKcs mRNA or polypeptide levels) to determine if cancer cells that are homologous recombination-deficient are likely to be susceptible or resistant to PARP inhibitors and platinating agents are provided.