A total of 31 consecutive patients with hematologic malignancies who were considered poor candidates for TBI underwent allogeneic stem cell transplantation after conditioning with fludarabine and melphalan. A total of 25 matched sibling recipients received fludarabine 25 mg/m(2) x 5 days and melphalan 70 mg/m(2) x 2 days. For unrelated and haploidentical donor recipients, fludarabine was increased to 30 mg/m(2) and ATG 30 mg/kg x 4 days was added. Graft-versus-host disease prophylaxis consisted of tacrolimus and mini methotrexate. All patients engrafted. Regimen-related toxicity was considerable and included mainly renal, hepatic and mucosal toxicity. There were seven regimen-related-deaths including two VOD, two pulmonary, one renal, one cardiac and one mucosal toxicity. One case of fatal pulmonary toxicity death could be attributed to pre-existing pulmonary damage. Progression-free survival at 12 months was 44% (90% CI: 30-58%) for recipients of HLA-identical sibling transplants and 33% (90% CI: 21-45%) for all patients. In conclusion, the fludarabine-melphalan regimen leads to consistent engraftment. The regimen-related toxicity is considerable and cannot be explained solely by patient selection. Cardiac toxicity is emerging as a unique toxicity of this regimen. Despite toxicity, fludarabine-melphalan has considerable activity and leads to durable remission in a proportion of patients.