Bone marrow transplantation (BMT) offers potentially curable treatment for patients with high-risk hematologic malignancies. However, relapse remains the major cause for failure of autologous BMT in these diseases and of allogeneic BMT in subsets of patients with these diseases. With our current preparative regimens, relapse rates following autologous BMT are over 30% for patients with intermediate or high-grade non-Hodgkin lymphoma and relapsed Hodgkin's disease in sensitive relapse and over 50% following autologous BMT for patients with acute non-lymphoblastic leukemia (ANLL) and acute lymphoblastic leukemia (ALL). Relapse rates exceed 80% in patients treated with autologous BMT for non-Hodgkin lymphomas and Hodgkin's disease in drug-resistant relapse. We also see a relapse rate over 50% in patients given allogeneic BMT for ANLL in second or third remission or early relapse, for ALL in third or subsequent remission or early relapse, and for chronic myelogenous leukemia (CML) in accelerated phase or blast crisis. We have explored two new approaches for improving the anti-tumor activity of our BMT preparative regimens. One involves combining etoposide, a chemotherapeutic agent that has excellent activity against leukemias and lymphomas, has shown synergistic activity with cyclophosphamide in vitro, and can be substantially dose-escalated, with busulfan and cyclophosphamide. The other approach attempts to induce graft-versus-host disease (GVHD), which appears to provide a clinical anti-tumor effect following allogeneic BMT, in recipients of autologous BMT. A syndrome similar to mild GVHD has been reported to occur spontaneously in a small number of patients receiving autologous or syngeneic transplants. GVHD can also be induced in rats undergoing syngeneic BMT by treatment with cyclosporine (CSA).(ABSTRACT TRUNCATED AT 250 WORDS)