The history of vaccine therapy in herpes simplex infection in man, employing both dead and live virus, has been disappointing. Even in the presence of circulating antibody attacks occur. Thus any new immunizing procedure admittedly must be viewed with considerable skepticism. Yet in the case of herpetic keratitis in which repeated attacks may lead to blindness, new ideas should be explored. Recent studies1 have shown that potent tissue culture vaccines, with excellent immunizing properties in experimental animals, deserve more than passing interest. Apart from this, past failures in attempted prophylaxis of the infection in man may be attributed to the failure to recognize the allergic phase of the disease. Thus it is not surprising that routine immunizing procedures consisting of three or four injections of vaccine material are ineffective. Tt is the object of this paper to explore the usefulness of tissue culture vaccine in preventing recurrent attacks of herpetic keratitis. Concomitantly the use of the antigen in the diagnosis of herpetic infections will be presented.