We have previously reported that fetal bone marrow (FBM) has higher number of CD34+ cells, greater clonogenic capacity, and lowered immunologic reactivity compared to adult bone marrow (ABM), cord blood (CB), and peripheral blood lymphocytes (PBL). The present studies were designed to investigate whether similar ontogenetic differences exist in the expression of hematopoietic-related cytokines by stromal cells from FBM, ABM, and CB using RT-PCR. Stromal cells were prepared in long-term cultures supplemented with hydrocortisone to 80% confluency from specimens obtained from 8 FBM (n=8), collected from spontaneously aborted fetuses at gestational age of 18-20 weeks; 8 ABM (n=8) from allogeneic donors; 7 CB (n=7) samples. RNA was extracted from the stromal cells and reverse-transcribed into cDNA which was then subjected to PCR using specific primers for stem cell factor (SCF), GM-CSF, G-CSF, M-CSF, IL-3, IL-6, IL-10, IL-11, respectively. Quantitation of products was measured by densitometry using a Howtech Scanner. A strong expression of SCF and IL-11 was observed in the stromal cells from FBM compared to ABM and CB. Although M-CSF was not detected in any of 8 FBM specimens, it was highly expressed in all ABM and CB samples. IL-6 was detected in 6/8 ABM but in only 1/8 FBM and 0/7 CB. Although G-CSF was not observed in CB, it was expressed in all FBM and ABM specimens. In contrast, expression of GM-CSF, IL-3, and IL-10 from different sources of stromal cells was similar. These results strongly indicate that there are age-related changes in cytokine expression in stromal cells at different maturational stages. Further, these results suggest an important role for these cytokines in their capacity to regulate differentiation and proliferation of stem cells during ontogentic development, and these may provide better predictive information for treatment of hematologic diseases as well as selection of stem cells for transplantation.