Incubation of herpes simplex virus (HSV) with papain-derived fragments (Fab) of rabbit anti-HSV γ globulin resulted in substantial virus neutralization. The infectious virus that survived incubation with the Fab fragments was found to exist in the form of an infectious virus-antibody complex (sensitized virus). Incubation of the sensitized virus with undigested sheep anti-rabbit γ globulin or the Fab fragments of sheep anti-rabbit γ globulin resulted in further virus neutralization. The specificity involved in the neutralization of sensitized virus by anti-γ globulin was shown by the fact that virus sensitized with undigested or papain-derived fragments of rabbit anti-HSV γ globulin of one allotype was neutralized by anti-γ globulin directed against that allotype but not by anti-γ globulin directed against a different allotype.