Forming and mature human placental coated vesicles contained thickened regions of glycocalyx which were absent from other regions of the cell surface. Over 98% of vesicles lay within the diameter of the largest vesicle from the cell surface. Negative staining confirmed earlier description of polygonally patterned structures on the cytoplasmic surface of placental coated vesicles based on goniometry of ultrathin sectioned material. A 180,000 MW protein from an isolated fraction of coated vesicles probably represented vesicle surface structure protein clathrin which had not previously been identified in any human or placental tissue.