Summary: The adoptive transfer of tumor-infiltrating lymphocytes (TH.) along with interleukin (H.)-2 into autologous patients with cancer resulted in the objective regression of tumor, indicating that T cells play an important role in tumor regression. In the last few years, efforts have been made towards understanding the molecular basis of T-cell-mediated antitumor immunity and elucidating the molecular nature of tumor antigens recognized by T cells. Tumor antigens identified thus far could be classified into several catagories: tissue-specific differentiation antigens, tumor-specific shared antigens and tumor-specific unique antigens, CD4 T cells play a central role in orchestrating the host immune response against cancer, infections diseases, and autoimmune deseases, and we thus have attempted to identify major histocompatibility complex (MHC) class II-restricted tumor antigens as well. The identification of tumor rejection antigens provides new opportunities for the development of therapeutic strategies against cancer. This review will summarize the current status of MHC class I- and class II-restricted human tumor antigens, and their potential application to cancer treatment.