Nine patients with haematological malignancy relapsed 3-32 months after receiving cyclophosphamide 120 mg/kg, 12-14 Gy fractionated total body irradiation and an HLA-identical sibling bone marrow transplant. They were reconditioned with melphalan 180-220 mg/m2 and retransplanted using the same donor and the same cyclosporin regimen as prophylaxis for graft-versus-host disease (GVHD). Three of the nine remain alive greater than 81, greater than 33, and greater than 36 months after second transplant. While the rate of marrow engraftment, the incidence of acute GVHD and the incidence of interstitial pneumonitis were similar after first and second transplants, the use of melphalan before second transplant was associated with increased nephrotoxicity and oropharyngeal mucositis. The present study shows that second narrow transplants are feasible, can produce prolonged remission of haematological malignancies and should be considered in appropriate patients who relapse after first marrow transplant.