The rearrangement of TCR-beta gene, one of the earliest events in T cell development, consists of two consecutive steps: D-J rearrangement and V-DJ rearrangement. The present study examined the signals supporting D-J beta and V-DJ beta rearrangements during early T cell development from progenitor cells that reside in fetal liver. We have found that there is an interval of 1 to 2 days between D-J beta and V-DJ beta rearrangements during the early T cell development from fetal liver progenitor cells in deoxyguanosine-treated thymus lobes. We have also found that IL-7, a cytokine expressed in the subcapsular area of the thymus, can promote D-J beta rearrangement of fetal liver progenitor cells, and that anti-IL-7 and anti-IL-7R Abs inhibit the D-J beta rearrangement and further T cell development of fetal liver progenitor cells in the thymus environment. Interestingly, unlike the thymus environment, IL-7 alone was not capable of supporting V-DJ beta rearrangement in the fetal liver cell cultures. These results indicate that D-J beta rearrangement during fetal liver-derived early T cell development is supported in the thymus by IL-7. Furthermore, the present results demonstrate that IL-7, supporting D-J beta rearrangement, does not promote V-DJ beta rearrangement of fetal liver progenitor cells, suggesting that intrathymic molecules promoting V-DJ beta rearrangement are distinct from IL-7 that supports the D-J beta rearrangement.