Infectivity of DNA isolated from L cells chronically infected with SV5 paramyxovirus was demonstrated by inoculation of continuous RH and HEp-2 cells. Infectivity of the DNA was completely abolished by treatment with deoxyribonuclease or by alkaline hydrolysis but did not change after treatment with ribonuclease and specific anti SV5 serum. The virus obtained as a result of transfection caused haemadsorption in susceptible cells and was neutralized by specific antiserum like the prototype SV5 strain.