The purpose of the study was to determine the feasibility and efficacy of a reduced intensity conditioning regimen of fludarabine and melphalan for allogeneic transplantation in patients with multiple myeloma. From August 1996 to December 2000, 22 patients received a reduced intensity conditioning regimen with fludarabine and melphalan. Median age was 51 years (range, 45-64), median time from initial therapy to transplant was 36 months (range, 3-135 months). Disease phase prior to transplant was primary refractory in two patients, refractory relapse in 11 patients, sensitive relapse in eight patients and initial remission consolidation in one patient. The median number of prior therapies was five (range, 1-7), and median beta 2 microglobulin prior to transplant was 3.0 mg/l (range, 1.0-7.3). All patients received unmanipulated grafts from either HLA matched sibling donors (n = 13) or matched unrelated donors (n = 9). Eighteen patients received fludarabine 30 mg/m(2) for 4 days with melphalan 140 mg/m(2) as a single dose and four patients received fludarabine 25 mg/m(2) for 5 days with melphalan 90 mg/m(2) daily for 2 days. All 21 patients evaluable for engraftment achieved a neutrophil count of >0.5 x 10(9)/l after a median of 12 days (range, 9-24), 18 patients achieved platelet transfusion independence after a median of 14 days (range, 8-47). All engrafting patients had 100% donor cell engraftment. Seven patients achieved a complete remission. Six patients are currently alive with a median follow-up of 15 months (range, 10-47 months). The actuarial survival and progression-free survival is 30 +/- 11% and 19 +/- 9% at 2 years. Non-relapse mortality at 100 days was 19 +/- 10% and 40 +/- 10% at 1 year. Fludarabine/melphalan combinations are feasible and allow consistent engraftment of allogeneic progenitor cells from both related and unrelated donors in patients with multiple myeloma and should be explored in patients with less advanced disease.