A phase variance optical coherence microscope (pvOCM) has been created to image blood flow in the microvasculature of zebrafish embryos, without the use of exogenous labels. The pvOCM imaging system has axial and lateral resolutions of 2.8 ?? ? m in tissue and imaging depth of more than 100 ?? ? m . Images of 2 to 5 days postfertilization zebrafish embryos identified the detailed anatomical structure based on OCM intensity contrast. Phase variance contrast offered visualization of blood flow in the arteries, veins, and capillaries. The pvOCM images of the vasculature were confirmed by direct comparisons with fluorescence microscopy images of transgenic embryos in which the vascular endothelium is labeled with green fluorescent protein. The ability of pvOCM to capture activities of regional blood flow permits it to reveal functional information that is of great utility for the study of vascular development.