The revelation that immune cytolytic and helper T-cells recognize intracellularly degraded peptides processed via the proteosome apparatus, inserted into the endoplasmic reticulum and transported to the surface for association with major histocompatibility locus (MHC) molecules on specialized antigen-presenting cells has revolutionized the cancer vaccine field. Understanding the science of antigen processing and presentation has provided new reagents, delivery systems, and new investigative leads for the generation of immune responses against cancer. The cloning of tumor antigen genes has proceeded rapidly in melanoma, due to the ease with which melanoma-specific T-cells can be propagated in vitro, but breast, cervix, and lung cancer are not far behind. The cloning and identification of tumor antigens recognized by T-cells and data from initial clinical trials with peptides vaccines derived from those antigens are presented.