Due to the availability of the endothelial cell marker QH1, experiments using quail embryos have traditionally been used to trace the endothelial cell lineage and describe the morphologic events of vessel formation. A comparable marker in the chicken has not been available. Here we report that antibodies raised against the extracellular domain of the chicken type II TGFbeta receptor (TBRII) preferentially identify endothelial cells in the chick. Endothelial cells can first be identified in the 6-somite chick embryo by TBRII expression. TBRII expression in 12- and 22-somite chick and quail embryos was found to directly correlate with the endothelial QH1 staining pattern in quail. This preferential labeling of endothelial cells persists until at least embryonic day 10 in the chick. These data indicate that antibodies to TBRII are an effective marker of endothelial cells in chick and provide useful reagents for the evaluation of vascular patterning.