We created a syngeneic mouse bone marrow transplantation (BMT) model to examine the effect of endogenous interleukin-7 (IL-7) on long-term (>or=140 days) haematopoietic reconstitution and survival after BMT. Wild-type (WT) IL-7(+/+) and knockout (KO) IL-7(-/-) mice were lethally irradiated and transplanted with bone marrow. Survival is best (85.7%) in the group WT grafts transplanted into WT recipients (WT-->WT) with a trend towards poorer survival in the other groups (WT-->KO: 60%, KO-->WT: 50%, KO-->KO: 45.5%, differences statistically not significant). If the recipient is deficient for IL-7-producing cells, T- and B-cell reconstitution remain incomplete. If the graft lacks IL-7-producing cells there is a significant delay in T- and NK-cell reconstitution. Interestingly, in the absence of IL-7, T-cell reconstitution is neither delayed nor incomplete because of an expansion of TCRalphabeta(+)/CD4(-)/CD8(-) double negative T cells. Long-term survival and lymphocyte reconstitution after syngeneic BMT can occur despite the absence of IL-7.