Glial cell differentiation in Drosophila melanogaster requires the activity of glide/gcm (glial cell deficient/glial cell missing). The role of this gene is to direct the cell fate switch between neurons and glial cells by activating the glial developmental program in multipotent precursor cells of the nervous system. In this paper, we show that glide/gcm is also expressed and required in the lineage of hemocytes/macrophages, scavenger cells that phagocytose cells undergoing programmed cell death. In addition, we show that, as for glial cells, glide/gcm plays an instructive role in hemocyte differentiation. Interestingly, it has been shown that in the development of the fly adult nervous system the role of scavenger cells is played by glial cells. These data and our findings on the dual role of glide/gcm indicate that glial cells and hemocytes/macrophages are functionally and molecularly related.