Herpes simplex viruses 1 and 2, two closely related members of the alpha herpes virus family, are common pathogens in the human population. Recurrent herpes simplex virus (HSV) infections produce clinical disease in a significant proportion of individuals who have been infected with either type of HSV. HSV-1 reactivation is manifest as herpes labialis, while HSV-2 reactivation causes herpes genitalis. The potential of interferons to alter the pathogenesis of HSV infections is of interest because of the known immunomodulatory and antiviral functions of these mammalian cell proteins. The addition of dibutyryl cyclic AMP blocked the induction of macrophage-mediated cytotoxicity, indicating that epinephrines affected macrophage function via an adrenergic receptor-mediated system.