The L3/T4+ and Lyt-2+ T-cell subsets can be depleted from mice, using selected monoclonal antibodies in vivo, at different times during rejection of, or priming to, allogeneic skin grafts. Although L3/T4+ cells are sufficient to reject skin grafts in naive Lyt-2-depleted mice, we show that Lyt-2+ cells can become involved, after an initial delay, in intact mice. Furthermore, these Lyt-2+ cells are primed to dominate the accelerated rejection of a normal secondary response. Mice depleted of L3...