This chapter summarizes the various epithelial ovarian cancer markers which have been termed cystadenocarcinoma 'antigens'. Virtually every reported antigen has been demonstrated by raising antibodies to tumour extracts injected into heterologous animals. As yet, despite numerous attempts, no heterologous antiserum has been demonstrated to have the requisite sensitivity and specificity for the immunodiagnosis of early ovarian cancer. However, some of the antigen markers may prove useful in monitoring the response to therapy. Hybridoma-generated monoclonal antibodies could prove to be the means by which the immunodiagnosis of early ovarian cancer will be achieved. That the abnormal antigens reflect altered glycoprotein metabolism is suggested by the findings of elevated serum galactosyltransferase, which in itself is a good ovarian cancer tumour marker, and a genetic serum deficiency of alpha-L-fucosidase, which appears to identify a high risk population for the development of ovarian cancer.