Allogeneic hematopoietic stem cell transplantation is often used to treat hematologic malignancies. The efficacy of this procedure is due to both myeloablative conditioning and graft-versus-leukemia (GVL). However, the disadvantages of allogeneic transplantation include graft-versus-host disease (GVHD), relapse from the original tumor, and patient susceptibility to opportunistic infections. Lately, allogeneic transplantation has been developed to treat solid tumors, with the expectation that graft-versus-tumor (GVT), like GVL, will have a significant anti-tumor effect. This effect has been demonstrated in renal carcinomas, and with less evidence in breast cancers. Five patients with malignant ovarian tumors resistant to chemotherapy underwent allogeneic transplantation, four from bone marrow, and one from peripheral blood stem cells. All donors were HLA-identical siblings. One patient received a myeloablative conditioning regimen, while the other four received a non-myeloablative regimen. Two patients received donor lymphocyte infusions (DLI). Four of the patients presented with acute or chronic GVHD associated with tumor regression of at least 50%. These tumor regressions were measured by CA-125 levels and CT scans. The fifth patient died of rapid progression just after transplantation. Of the four transplantation survivors, three received a non-myeloablative regimen which did not seem to reduce treatment effectiveness. While it did reduce toxicity, one of these patients died of GVHD after 127 days. DLI was administered to two patients. These infusions seemed to promote GVHD which was able to control disease progression for one patient and had no apparent effect on the other. Allograft of hematopoietic stem cells might be of interest in ovarian cancer. The results in one patient also suggest that DLI may be an effective immunotherapy, although doses and timing need to be determined. The number of cases presented is small, however, and clinical experience on a larger scale will be required to determine the real clinical efficacy of graft versus cancerous ovarian cells.