The basement membrane is a structure of prime importance for the proper functioning of certain organs such as the lens and the kidney. Its inaccessibility and resistance to extraction, however, make an absolute determination of its composition difficult. The establishment of a cell line that synthesizes authentic basement membrane components in vitro would make basement membrane components more easily obtained, and would provide a controlled situation which could be more easily manipulated. In this report, a Balb/C mouse lens epithelial cell line was investigated. The cells were observed to undergo morphological transformations in vitro depending upon the cell density. As cell-cell contacts became prevalent, stellate cells organized into an epithelioid sheet. Later, elongate cells and lentoid bodies predominated in the culture. Thus, morphologically the cells mimicked the in vivo transition of the lens epithelial cells into lens fiber cells. Furthermore, the collagen(s) synthesized by these cells reacted specifically with affinity purified antibody directed against mouse type IV collagen. These morphological and immunological data lend credence to the concept that this lens epithelial cell line is an authentic replica of the in vivo situation.