A HSV-specific, Lyt 1+2- T cell clone (D7.1) was established by repetitive in vitro restimulation of in vivo HSV-1 primed draining lymph node cells with UV-inactivated homologous virus. Earlier work had shown that this clone could provide specific helper activity for HSV-1 primed B cells for antibody production in vivo. In this paper, further functional analysis has demonstrated that this clone and its subclones could also help unprimed T cells in the generation of effector DTH T cells in vitro. The helper activity was found to be antigen-specific and cell dose-dependent. In addition, this helper T cell clone showed little, if any, natural killer-like activity and was non-cytolytic towards both HSV-infected and uninfected syngeneic targets. However, they could exert potent cytotoxic activity towards P815 and EL-4 tumour targets in the presence of lectins.