The cryopreservation and long-term culture of fetal liver (FL) cells may offer a ready source of haematopoietic stem cells (HSC). To compare these two techniques, an H-2-incompatible murine model was used, in conditions close to those of stem cell transplantation in humans. After cryopreservation, the recovery of colony-forming unit-culture (CFU-C) and of 14-day colony-forming unit-spleen (CFU-S) was 55.5% and 23%, respectively, compared with fresh cells. The rate of engraftment of donor cells was very high in mice reconstituted with either cryopreserved or fresh cells and the resulting chimerism was virtually complete in both cases. Functionally, both groups showed a significant humoral response to sheep red blood cells. Chimeric mice obtained by injection of cryopreserved cells were able to reject third-party SJL mouse (H-2s) skin grafts (11.4 +/- 1.6 days); at the same time, they specifically tolerated skin grafts from BDF1 (H-2b x H-2d) donor mice, indicating that cryopreserved FL cells could induce both tolerance to donor antigens and restore normal immunological responses to third-party alloantigens. Following 4-week cultures, consistent losses in the total number of CFU-C and CFU-S (2.5% and 8.6% yield, respectively) were observed. Cultured FL failed to protect the animals from the lethal effects of irradiation, due to insufficient reconstitution. These results favour the possible use of cryopreserved FL in clinical settings. At present, however, techniques to improve FL cultures and their efficiency for in vivo reconstitution are required.