The development of diabetes mellitus in mice by viruses was determined. Infection of mice with M variant of encephalomyocarditis virus produced a diabetes mellitus. A number of other viruses including cytomegalovirus and coxsackie virus have been suggested for the association with the onset of the disease. Mumps virus, mengo virus, herpes simplex virus type I and type II were determined for the association with diabetes mellitus in mice. But those viruses have not been associated with diabetes mellitus in mice. It is concluded that the development of diabetes mellitus in mice is restricted to the specific virus which has the ability of replication in the pancreatic beta cells.