A number of monoclonal antibodies (Mabs) have been produced in mice using peptides of mucins (MUC1, MUC2, MUC3 and MUC4), which react with native molecules expressed in cancers. Their epitopes were mapped using Pepscan method and found that most epitopes consisted of 3-6 amino acids. In addition, T cell immune responses have been generated to mucins in mice and their epitopes have been mapped. Furthermore, in human clinical trials both antibody and cellular responses can also be generated using mucin peptides. Mabs and T cells to mucin peptides can be of diagnostic or therapeutic value.