ferons in vivo. Sources of this interferon have included lungs of mice infected with influenza virus (Isaacs and Hitch-cock, 1960), brains of mice infected with O'nong-O'nyong virus (Hitchcock and Porterfield, 1961), the skin of guinea pigs infected with vaccinia virus (Friedman et al, 1962), various tissues of mice of different ages infected with Coxsackie Bl virus (Heineberg et al, 1964), and blood samples from human volunteers injected with an Asian strain of influenza virus (Jao et al, 1965). While the present work was in prog-ress, Force et al (1965) reported the production of interferon in the skin of rabbits infected with herpes simplex virus (HSV). These workers demon-strated that peak interferon titers closely followed the peak production of virus in the tissues and that peak anti-body production occurred much later, after viral concentrations had decreased. Wheelock and Sibley (1965) reported a similar finding in human volunteers injected with the 17D strain of yellow