This study involves the characterization of the primates polyomaviruses BK, JC, SV40, STMV, and SA12. Each of these polyomaviruses is oncogenic in hamsters and can transform certain rodent cells in culture. BK and JC are each human polyomaviruses. The purpose of this work is to better characterize BK and JC at a biologic and molecular level to better understand their potential roles in human disease.