SUMMARYIntraperitoneal (i.p.) immunization with herpes simplex virus type 1 (HSV-1) or an anti-idiotypic antibody (anti-id C) prepared against a monoclonal antibody specific for glycoprotein C of HSV-1, tolerizes mice for an HSV-I delayed type hypersensitivity (DTH) response. This tolerization could be adoptively transferred to naive Xirradiated mice by splenic T cells, and was specific for HSV-1 DTH. Thus, DTHtolerized mice responded to vaccinia virus or HSV-2 challenge, while remaining tolerized for HSV-1 DTH. In addition, these animals demonstrated a form of split tolerance such that HSV antibody, cytotoxic T cell and lymphoproliferative responses were detected in vitro. Thus, anti-id C induced a T cell population capable of specifically suppressing the HSV-1 DTH response, mimicking the effect of i.p. and intravenous immunization with HSV-1 found previously.