Vitamin D metabolites have multiple functions not only in calcium homeostasis, but also in hematopoiesis. To detect the effect of vitamin D on hematopoiesis with a surface glycoprotein marker, the proportions of the CD34+ cells were measured in bone marrow, peripheral blood and spleen prior to and after vitamin D3 treatment in an infant with severe rickets, myelofibrosis and myeloid metaplasia. CD34+ cells measured 0.4% in bone marrow, 8.0% in peripheral blood and 8.7% in splenic aspirate. The detection of a high and comparable level of CD34+ cells in both peripheral blood and splenic aspirate on admission and the decline in the level of CD34+ cells (2%) following treatment support that CD34+ cells were from extramedullary hematopoiesis in spleen. The improvement of rickets and hematological findings with treatment at the same time raises the possibility of vitamin D3 acting directly upon the same target or upon different targets at the same time or of the presence of interaction between two targets. Our findings may also show a relation between vitamin D3 and its metabolites to bone marrow stem cells.