The idea that there might be an immune response to cancer has been around for many years. Immunotherapy has a long history, but is only rarely considered as the treatment of choice. Immunotherapy has encountered a number of intrinsic difficulties in cancer, such as the antigenic resemblance between the tumour and normal cells, the rapid kinetic proliferation of tumour cells and their reduced immunogenicity. There are various types of immunotherapy. Aspecific immunotherapy augments the body s immune response without targeting specific tumoral antigens. In adoptive immunotherapy, cells are administered with antitumoral reactivity to mediate neoplasm regression. Specific active immunotherapy is based on the principle that neoplasm cells contain immunogenic sites against which an antitumoral immune response can be induced in an attempt to stimulate the immune system to target specific tumoral antigens. Vaccines against cancer cells are based on a more precise identification of the tumoral antigen components. Passive immunotherapy was limited by the difficulty of obtaining high titering and specificity in early attempts using polyclonal antisera; monoclonal antibodies are currently used alone or in association with radioactive substances and cytotoxic agents. Enormous progress has been made this century in the use of immunotherapy for cancer treatment. It seems likely that the next century will see its increased afficacy, making it one of the possible therapeutic options.