Between August 1998 and July 1999, 21 patients received a novel protocol of reduced conditioning with fludarabine, carmustine and melphalan (FBM) followed by matched-related allogeneic peripheral blood stem cell transplantation (PBSCT) in a prospective multi-center phase I/II study. Cyclosporin A and 'mini-methotrexate' were used for GVHD prophylaxis. Patients were included because of age, advanced disease, previous transplantation or co-morbidity. Hematopoietic engraftment after allogeneic transplantation was rapid with a median white blood count (WBC) >1 x 10(9)/l on day +11 (range 10-17) and a median platelet count >20 x 10(9)/l on day +13 (range 9-36). Donor chimerism was complete in 16/21 (76%) patients at all time points during follow-up and mixed at least on one occasion in 5/21 (24%) patients. The conditioning regimen was well tolerated with low toxicity even in previously transplanted patients. Thirteen patients (62%) developed acute GVHD grades II-IV. Nineteen out of 21 patients achieved complete (CR, n = 15) or partial remission (PR, n = 4) with a median patient follow-up of 354+ days (range 258-577) for patients alive. The reduced intensity protocol FBM is feasible with rapid engraftment, early achievement of complete donor chimerism, low toxicity, especially in heavily pretreated patients, and good response rates in advanced disease patients.