HCG and its subunits alpha and beta are produced by trophoblastic cancers constituting an index of early detection and monitoring for these tumors. Unlike HCG-alpha, we can obtain specific HCG and HCG-beta assays with LH-neutralized antiserum. Many normal non-trophoblastic tissues exhibit a HCG-like immunoreactivity. All choriocarcinomatous testicular tumors produce HCG and HCG-beta. Half of all testicular teratomas produce HCG and its subunits while a third of all seminomas exhibit an HCG-like immunoreactivity, whether choriocarcinomatous component is present or not. Serum HCG levels are elevated in seminomas (5 to 22%) as well as teratomas '55 to 89%). Less than 15% of breast, digestive and lung cancers have increased serum levels of HCG and/or its 2 subunits. HCG is most often produced by undifferentiated lung cancers, hepatoblastomas and adrenal carcinomas. There is usually a parallel relation between these serum levels and the clinical evolution of the disease under chemotherapy. In breast cancer, these levels do not constitue a "prognosis index". HCG production by non-trophoblastic tumors can induce clinical symptoms such as precocious puberty and gynecomastia.