Summary Mild trauma was induced in the skin of mice latently infected with herpes simplex virus type 1 by stripping the originally infected ear with cellophane tape. Recurrent herpes simplex developed at this site 2 to 5 days later. It was detected clinically by the development of erythema and vesicles and by the appearance of virus in the skin. On any one occasion about 30% of mice showed reactivated disease and increasing the severity of trauma did not increase this proportion. However the majority of animals developed reactivated disease on some occasions when stripping was repeated at monthly intervals. The results are discussed in relation to the skin trigger theory of reactivation of herpes simplex.