During the reproductive period, mothers and offspring exchange hematopoietic cells and develop a form of immunological tolerance bidirectionally. To examine whether previous experience of such communication has any remote effect when maternal hematopoietic cells are later transplanted to the children, we retrospectively compared the outcomes of blood and marrow stem cell transplantation from maternal donors (n = 46) to those from paternal donors (n = 50) by using the database of the Japanese nationwide surveys for adult hematopoietic cell transplants between 1990 and 1998. At 5 years, recipients of maternal hematopoietic cells had a significantly higher overall survival than patients receiving paternal grafts (60% vs 32%, P = 0.006). Although no significant difference was observed in the occurrence of severe acute GVHD (grade > or =III) and the relapse of malignant diseases between two groups, the probability of non-relapse treatment-related mortality was significantly lower after maternal donor transplants. Furthermore, multivariate analysis revealed that parental donor type was the only factor significantly associated with overall survival. In conclusion, our analysis indicates superior survival of maternally donated recipients in hematopoietic stem-cell transplantations from biological parents. This finding has important implications in the selection of alternative familial donors, and warrants further prospective analysis of parental donor transplantations.