The cancer literature contains many tantalising suggestions that immune responses may be important in the control of cancer. It is only recently that human cancer antigens have been discovered and techniques have become available to study these responses. The ยฎrst human cancer antigens were deยฎned as T cell targets, involving laborious screening of cells from cancer patients exhibiting immune responses against their tumours. SEREX technology takes advantage of the presence of circulating antibodies against various cancer antigens and allows relatively rapid deยฎnition of the antigen. Over 1500 protein antigens are now listed in the SEREX database. Improved understanding of the processes underlying immune recognition and control of the immune response against these antigens is now bearing fruit in the form of clinical trials in cancer patients. The most mature of these studies involve monoclonal antibodies and in some cases these treatments are now marketed. T cell responses have been targeted using peptide antigens as ``vaccines''. Other antigens such as whole recombinant proteins or glycolipids are now also being investigated. Cancer vaccine studies were performed initially in patients with advanced disease. However, since responses against these antigens may take several months to develop, it is not surprising that many of these patients require other treatment before any immune response can be detected. Some investigators are now studying patients with earlier stages of disease but who are at a signiยฎcant risk of relapse. Since these patients have no measurable disease, it is increasingly important to have well-validated and reproducible immunological surrogate assays as endpoints for these studies. Once the optimal method of immunisation is deยฎned it will then be possible to move back into the more difยฎcult group of patients with advanced disease. There is also the prospect of offering adjuvant therapy, when immune responses might be expected to be of most use.