In intimate contact with epithelial tissue is the extracellular matrix that forms a highly specialized condensed layer known as the basement membrane. The is supramolecular structure involves type IV collagen and laminin 5 is known to provide physical support for the epithelial tissue overlying it. In this study we examine other proposed role(s) of these molecular structures and their receptors during skin development using the mammary gland as a model. The pattern of expression of these molecules during skin formation was examined using immunohistochemistry, utilizing collagen IV, laminin 5 and β4 or α6 integrin antibodies. The dissected mammary glands were also examined by transmission electron microscopy. Our results suggest that these supramolecular structures play important roles in skin derivative development, more specifically mammary gland formation, of these roles; they ease their resistance to skin derivatives down growth (invasion) into the under laying tissue.