Human papovavirus JC is to be studied biochemically to ascertain the mechanism whereby it induces a high frequency of brain and other tumors in hamsters. The viral DNA will be labeled in vitro and used as a probe to identify viral sequences in tumor cell DNA, and comparison of JC and SV40 induced tumors will be done to see if the demonstrable homology of portions of their genomes is pertinent to the oncogenic process. These studies will provide the positive controls necessary to probe for JC DNA sequences in various human tumors of unknown etiology. BIBLIOGRAPHIC REFERENCES: Comparison of JC and BK human papovaviruses with SV40: DNA homology studies. J.E. Osborn, S. Robertson, B. Padgett, D. Walker and B. Weisblum. J. Virol. (In press, August, 1976).