Summary—The basement membranes elaborated by corneal epithelium in the chick embryo and in culture conditions have been studied by quick‐freezing and deep‐etching methods. Electron microscope observations ofen faceunidirectional platinum shadow castings revealed a polygonal network comparable to the type IV collagen network described in human amniotic basement membrane and EHS mouse tumor matrix [22]. The material deposited in culture contained type IV collagen, as demonstrated by immunofluorescence labeling using anti‐type IV collagen antibodies and formed delicate networks. Fine filaments and granules composing this network were interpreted respectively as linear and globular NCI domains of the type IV collagen molecule. These loose networks were considered as first steps in basement membrane assembly. Staggered superimposition of comparable networks could lead to the dense network organization as observed for basement membranesin situ. These observations showed that the basement membrane of the chick embryo corneal epithelium is also organized in a complex polygonal framework that is preserved even when secreted in cultrue con