Ultrastructural immunocytochemical characterization of human long-term bone marrow cultures has shown positive localization for growth factors on cell surface and on extracellular matrix（ECM）.In some cases double-labelling indicated co-localization of growth factors and specific cell surface labels.Specific markers for endothelial cells and fibroblasts showed that growth factor（GM-CSF

G-CSF and b-FGF） were present at the surface of these cell types.Both scanning and transmission electron microscopy indicated intense labelling for growth factors on the extracellular matrix.Double-labelling of heparan sulphate proteoglycans and GM-CSF showed a co-localization of the labelling

which indicated the binding of growth factor to the extracellular matrix.