The behaviour of hematopoietic cells is influenced by their microenvironment. These "niches" are composed of variety of cells, including stromal cells. As cells mature, they move from one niche to another within the bone marrow until they are released into the periphery. To further understand these interactions, we will utilize a novel, non-invasive computer-driven microscopy program to visualize the interaction of blood cells with stromal cells at the single cell level.Stromal cells lines have been previously generated from fetal liver and one such cell line has been shown to support primitive blood cells. We will directly compare the interaction of immature and mature blood cells on this stromal cell line and other stromal cell lines that d o not maintain immature blood cells. By doing this, we hope to understand how hematopoietic cells behave on these cells and what interactions occur to keep blood cells immature, or how they are induced to mature.To further understand the factors involved in the interaction of blood cells with different niches, we will introduce the expression of growth factors into stromal cells and assess their effect on hematopoietic differentiation and movement. We will also eliminate the expression of growth factors to find out the effect of the loss of these proteins on blood cell behaviour.