Several tumors of murine origin produce a protein factor which neutralizes a distinct DNA polymerase (referred to as R-1 polymerase) which we have isolated from a murine myeloma line. In vivo, this inhibitor can be detected in the sera of tumor-bearing mice where its concentration is proportional to the extent of tumor growth. The purpose of this proposal is to isolate this inhibitor in quantity, characterize it chemically, and produce a specific antibody against it. Using this antibody, we propose to develop a radioimmunoassay for detection of this DNA polymerase inhibitor as a prototype for development of a highly sensitive tumor detection assay. In addition, a search will be carried out for analogous inhibitors in the serum of patients with leukemia and other lymphoid-type malignancies.