the present invention discloses a biologically active basement membrane composition . when polymerized under physiogical conditions , the composition forms gel - like structures whose ultrastructure resembles interconnected thin sheets of the lamina densa zone of basement membrane . the major components of the composition include laminin , type iv collagen , heparan sulfate proteoglycan , entactin and nidogen . these components polymerize in constant proportions when redissolved and allowed to reconstitute . molecular sieve studies on the soluble extract demonstrate that laminin , entactin and nidogen are associated in a large but dissociable complex . the reconstituted matrix is biologically active and stimulates the growth and differentiation of a variety of cells , including epithelial cells , nerve cells , hair follicles and the like . the reconstituted matrix can also be used for determining metastatic potential of tumor cells and for isolating metastatic tumor cells .