Poster Presentations -Session II transplantation (SCT) for lymphomas and the engraftment of donor immnnocompetent cells is essential.The height of host "immunological barrier" belongs to the major factors influencing engraftment.Some patients transplanted after non myeloablative regimens finally reconstituted their own immunocompetent cells because of insufficient immunosuppression and there has been no room for GvL effect.On the other hand, many pretrcated immunocompromised recipients developed severe complications due to unnecessary toxicity.11 patients with non-hodgkin lym pbomas (NHL -8x) and chronic lymphatic leukemia (CLL -3x) underwent non-myeloablative allogeneie SCT fronl sibling donor.No one of them was in complete remision (CR) before SCT.The recipients with the pretransplant level of CD3+ cells below than 0, 5x10 9/L were grafted after conditioning combined flndarabin (125rag/m2) and cyclophosphamide (120mg/kg).Those ones with CD3+ cells above 0, 5x10 9/L underwent SCT after fludarabin and melphalan (140rag/m2), fludarabin, melphalan and ATG (40mg/kg)or fludarabin, cyclophosphamide and ATG.The "graft versus host disease" (GvHD) prophyla~s consisted of cyclosporine A (CsA) only or CsA combined with the short-course of methotrexate (MTX).Donor chilnerism was evaluated in T-cell population at day +30, +60, +100 after SCT.CsA tapering depended on the grade of donor chimerism in T-cells. 10 patients (90, 0%) achieved complete donor chimerism in T-cells and sustained CR of their disease at the posttransplant follow-up period (median 134 days).6 recipient (54, 5%) developed GvHD.3 patients (27, 3%) died of transplant-related complications.The combination of fludarabin and cyclophosphamide (+/-ATG) was associated with significantly lower to, city and allowed sufficient engraftment of donor cells with effective immunological mmour control in severe immunocompromised hosts.The reduction of conditioningorelated to,city without the decrease of CR rate fully advocate the pretransplant evaluation of T-cell populations in recipients.