The present invention relates to a method for diagnosing leukemia, pre-leukemia or aleukemic malignant blood diseases, a method of discriminating leukemia from pre-leukemia or aleukemic malignant blood diseases, a method of discriminating aplastic anemia from myelodysplastic syndrome, a method of diagnosing delayed engraftment of the hematopoietic stem cells after transplantation of the hematopoietic stem cells, and a method of diagnosing the graft versus host disease, each of said methods comprising quantifying stem cell growth factor (SCGF). The present invention also makes it possible to provide an agent for diagnosing leukemia, pre-leukemia or aleukemic malignant blood diseases and an agent for diagnosing delayed engraftment of the hematopoietic stem cells after transplantation of the hematopoietic stem cells or an agent for diagnosing graft versus host disease (GVHD), each containing as an active ingredient an antibody reacting with stem cell growth factor (SCGF).