Metallopanstimulin (MPS) is a 9.5-kDal subunit "zinc finger" protein which is expressed in a wide variety of actively proliferating cells and tumor tissues (J. Biol. Chem. 268:21198-21204, 1993; Cell Growth & Diff. 5:811-825, 1994). A sensitive and specific radioimmunoassay (RIA) has been developed to measure circulating levels of MPS and MPS-like proteins. The RIA was evaluated for its ability to detect accurately elevations of MPS-immunoreactive material in the blood of patients with various types of neoplastic diseases. MPS concentrations were determined in the blood of 147 healthy subjects having no evidence of neoplastic disease, in 260 patients with nonmalignant diseases, and in 225 patients diagnosed with various types of cancer such as prostate, colorectal, lung, head and neck (epithelial malignancies), neuroendocrine, central nervous system, etc. Elevated MPS levels identified patients with neoplasias with greater than 90% confidence. In patients, not having neoplastic disease the MPS levels were lower than 10 ng/mL (82% of the population). In untreated patients with cancer, the MPS level range was 20-50 ng/mL and in stage M1b (metastasis to the bones) the MPS levels were extremely high (100 to 1000 ng/mL). In M1b patients that did not respond to therapy, the MPS levels remained very high ( > 100 ng/mL). In M1b patients that went into remission after treatment, the MPS levels were reduced. The MPS test may be useful as an aid in: 1) the early detection of a wide variety of neoplastic conditions and 2) the prognosis and management of cancer patients by following the changes in the concentrations of MPS in sera. Moreover, the results suggest that the combined use of the MPS test with other currently available tumor maker tests may significantly improve the chances of identifying a large proportion of active oncogenic processes by serodiagnosis.