Because zebrafish embryos are transparent, cell behaviors and interactions can be directly imaged noninvasively in live embryos using differential interference contrast-Nomarski light microscopy. We found that the imaging quality can be much improved by coupling differential interference contrast-Nomarski to true (analogical) color video so as to visualize the image in real time on a high-resolution colour video monitor. We explain here how to apply this approach to the in vivo imaging of embryonic macrophages, which constitute a distinct early macrophage lineage, that originates from the rostral-most lateral mesoderm--adjacent to the cardiac field, differentiate in the yolk sac, and rapidly spread in embryonic tissues, although still retaining proliferative capacity.