Abstract
A cytopathogenic effect has been observed in cultures of murine malignant lymphoma cells (strain P388 D1) inoculated with polyoma virus. There is evidence of viral multiplication in these cell cultures and the virus retains its ability to produce tumors when inoculated into newborn hamsters. The virus-host cell system of polyoma virus and milk-adapted P388 D1 cells seems to be a suitable one for studies of this oncogenic agent.