Transfusion with donor blood before transplantation can prolong the survival of renal allografts in the rat. The phenomenon is donor specific. We have investigated the effect of blood transfusion on both lymphocyte proliferation and the generation of donor-specific cytotoxic cells. In the first instance the kinetics of the proliferative responses of lymph node, spleen and thoracic duct lymph (TDL) leucocytes (harvested 7 days after transfusion of donor-specific blood, third-party allogeneic blood, syngeneic blood or no treatment) to lymph node stimulator cells were determined in a one-way mixed lymphocyte culture (MLC). Four strain combinations (LEW to DA, LEW to PVG, PVG to DA and DA to PVG) were investigated in this study. Maximal proliferation was observed at 4 days in the MLC and this was not altered by prior blood transfusion. When lymph node and TDL cells from transfused recipients were used as responders and stimulation was provided by cells from the same strain of rat as the blood donor, there was a significant depression of the MLC response compared to the response of cells harvested from untreated animals or animals given a syngeneic blood transfusion. This correlated with the behaviour of renal allografts in the same strain combinations. Lymph node and TDL cells harvested from rats that had received a third-party blood transfusion produced variable results in the MLC, ranging from a normal to a depressed response. No prolongation of allograft survival was noted in any animals pretreated with third-party blood. In contrast, when spleen cells were used as responder cells there was a donor-specific increase in the proliferative response on Day 4 in all strain combinations tested. In the second instance, specific cytotoxic activity was generated by in vitro (MLC) stimulation of lymph node or TDL, but not spleen, cell responders harvested from transfused or untreated rats. The activity of cytotoxic cells generated in MLC was quantified in a 51Cr-release assay, using Con A blast lymph node target cells prepared from animals of the same strain as the blood donor or a third-party strain. The specific cytotoxic activity generated was significantly increased when the responding cells were harvested from an animal that had received a donor-specific transfusion and then been restimulated by the blood donor in MLC.(ABSTRACT TRUNCATED AT 400 WORDS)