Recovery and migration of T-cells from the thymus to the secondary lymphoid organs in mice after sublethal gamma irradiation were investigated by measuring T-cell receptor excision circles (TRECs). The TRECs level practically represents the cellularity of thymus, in particular it correlates with the quantity of T-cells which have rearranged TCR genes and express the receptor complex CD3-TCR. So, TRECs can be considered as one of the markers of these cells. TREC-containing cells form a subset of recent thymic emigrants in the secondary lymphoid organs. After a significant TREC decrease in the lymph nodes within the early phase (4 days) after irradiation, we registered the increase of their number during urgent organ recovery due to T-cell migration from the thymus (the maximum is on the 10th day). The secondary thymic atrophy is accompanied by a weakening migration of the T-cells containing TRECs to lymph nodes. A significant TREC increase in the spleen was registered on the 4th day after irradiation. The rest of the recovery period. (up to 60 days) is characterized by the low TREC level. Thus, determination of TREC level allows obtaining additional information about recovery and migratory processes in lymphoid organs during post-radiation regeneration.