Summary:Relapse is a serious complication following high-dose therapy and autologous bone marrow transplantation (ABMT) for malignant lymphoma (ML). Allogeneic transplantation (alloSCT) is a therapeutic option. However, it is associated with a high incidence of transplantrelated organ toxicity and mortality. We recently reported fast engraftment and minimal transplantrelated toxicity, using fludarabine-based conditioning with reduced amounts of chemotoxic drugs prior to alloSCT. We now present our experience with 23 heavily treated high risk ML patients who underwent matched alloSCT following the same low intensity conditioning. The patients (20 male, three female) were aged 13-63 years. Nineteen had NHL and four HD (resistant disease 12, partial remission 11). Five were post ABMT. Twenty-two patients had fully matched sibling donors, and one a fully matched unrelated donor. Engraftment was fast. There was no rejection or nonengraftment. Organ toxicity was moderate with no liver or renal toxicity Ͼgrade II. Four patients developed Ͼgrade II graft-versus-host disease (GVHD). Seven patients died -four of grade III-IV GVHD and severe infections, two of bacterial sepsis, one of pulmonary failure. Ten patients are alive after 22.5 (15-37) months. Survival and disease-free survival at 37 months are both 40%. Probability of relapse is 26%. These encouraging results suggest that alloSCT following fludarabinebased low intensity conditioning in high-risk patients merits further evaluation. Bone Marrow Transplantation (2000) 25, 1021-1028. Keywords: allogeneic; peripheral blood stem cell transplantation; malignant lymphoma; fludarabine; low intensity conditioning regimen High-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (ASCT) has gained widespread acceptance as the treatment for aggressive nonHodgkin's lymphoma (NHL) in chemosensitive relapse,