By serially measuring serum levels of alpha-1 microglobulin and beta-2 microglobulin following allogeneic bone marrow transplantation (BMT), we tried to define their relationship to renal dysfunction, acute graft-versus-host disease (GVHD) and infection as complications of the transplantation. The study involved a total of 25 patients with leukemia, myelodysplastic syndrome and aplastic anemia who received BMT in this department; one patient received re-transplantation, thus bringing the total number of transplants to 26. Twenty-four patients received BMT from HLA-identical siblings while two others received BMT from unrelated donors. Alpha-1 microglobulin was within normal limits in all patients before BMT; among various complications such as nephrotoxicity, acute GVHD and infection which took place after transplantation, a raised alpha-1 microglobulin level was found only in nephrotoxicity; however, the increase was not significant compared with the pre-transplantation level. The pre-transplantation beta-2 microglobulin level was higher than normal in some patients; it was significantly increased in all of the above complications compared with the pretransplantation level (1.57 +/- 0.57 mg/l). A significant correlation was found between the serum creatinine level and the beta-2 microglobulin level (r = 0.849) in patients with renal dysfunction. In some patients, however, the beta-2 microglobulin level increased earlier than the serum creatinine level, and this finding was considered useful for the early diagnosis of renal dysfunction following allogeneic BMT.