C3H/HEJ mice injected with irradiated multiple minor incompatible B10.BR lymphoid cells via the portal vein showed delayed rejection of subsequent B10.BR skin grafts. Similar delayed rejection was produced by lateral tail vein injection of B10.BR hepatic mononuclear cells or H-2k cells pulsed in vivo with B10 minor histocompatibility antigens. Inhibition of C3H anti-B10.BR immunity in vivo (assessed by delayed graft rejection) and in vitro (assessed by B10.BR-induced lymphokine production) can be transferred by radioresistant, plastic-adherent F4/80+33D1-CD4-CD8-alpha beta TcR-gamma delta TcR- mononuclear hepatic cells from (C3H/HEJ x C3H.SW)F1 mice injected 36 hr earlier with 100 x 10(6) irradiated spleen cells. By 10 days post-injection, cells transferring delayed rejection are radiosensitive, plastic non-adherent, F4/80-33D1-CD4-CD8- alpha beta Tc+- gamma delta TcR+ cells. Injection of interleukin-2 (IL-2) in vivo into mice receiving pretreatment with B10.BR cells via the portal vein, or adoptive transfer into such mice of immune anti-B10.BR lymphoid cells, abolished delayed rejection on subsequent skin grafting. Delayed rejection or modulation of lymphokine production was associated in all cases with suppression of IL-2 production and preferential retention of IL-4 production from cells stimulated in vitro.