Monoclonal antibody-purged autologous bone marrow transplantation therapy for multiple myeloma. Eleven patients with plasma cell dyscrasias underwent high-dose chemoradiotherapy and anti-B-cell monoclonal antibody (MoAb)-treated autologous bone marrow transplantation (ABMT). The majority of patients had advanced Durie-Salmon stage myeloma at diagnosis, all were pretreated with chemotherapy, and six had received prior radiotherapy. At the time of ABMT, all patients demonstrated good performance status with Karnofsky score of 80% or greater and had less than 10% marrow tumor cells. Eight patients had residual monoclonal marrow plasma cells and 10 patients had paraprotein. Following high-dose melphalan and total body irradiation (TBI) there were seven complete responses, three partial responses, and one toxic death. Granulocytes greater than 500/mm3 were noted at a median of 21 (range 12 to 46) days posttransplant (PT) and untransfused platelets greater than 20,000/mm3 were noted at a median of 23 (12 to 53) days PT in 10 of the 11 patients. Natural killer cells and cytotoxic/suppressor T cells predominated early PT, with return of B cells at 3 months PT and normalization of T4:T8 ratio at 1 year PT. Less than 5% polyclonal marrow plasma cells were noted in all patients after transplant. Three of the seven complete responders have had return of paraprotein, two with myeloma, and have subsequently responded to alpha 2 interferon therapy. Eight patients are alive at 18.9 (8.9 to 43.1) months PT and four remain disease-free at 12.3, 17.5, 18.9, and 29 months PT. This preliminary study confirms that high-dose melphalan and TBI can achieve high response rates without unexpected toxicity in patients who have sensitive disease, and that MoAb-based purging techniques do not inhibit engraftment. Although the follow-up is short- and long-term outcome to be determined, relapses post-ABMT in these heavily pretreated patients suggest that ABMT or alternative treatment strategies should be evaluated earlier in the disease course. 