AbstractInjection of (CBA × A)F1cells into neonatal CBA mice rendered them tolerant to skin grafts of (CBA × A)Fi origin. Limiting dilution analysis revealed a very low frequency of tolerogen‐inducible cytotoxic T lymphocyte precursors (CTL‐P) in spleens of tolerant mice. Twoin vitroprocedures allowed, however, the induction of tolerogen‐specific CTL‐P of high frequencies in tolerant mice: (a) the “by‐pass” activation of spleen cells from tolerant mice by concanavalin A under short‐term bulk culture conditions followed by culture of limiting numbers of activated responder cells, and (b) absorption of spleen cells from tolerant mice on monolayers of tolero‐gen‐activated T cells from normal syngeneic mice. Furthermore, spleen ceils from tolerant mice, recently challenged with a tolerogen ‐ bearing skin graft, specifically suppressed the activation of tolerogen ‐ reactive splenic CTL‐P from normal CBA mice under limiting dilution conditions. These data confirm the presence of tolerogen‐specific CTL‐P of high frequency in tolerant mice and suggest their functional inactivation