Collagen and/or procollagen was demonstrated on the surface of monolayers of fibroblasts from normal rat kidney by indirect immunofluorescence with affinity-purified antibodies to collagen. The protein was arrayed in a reticular fashion on the cell surface and, in cells attached to a substratum, was severely restricted in its ability to undergo antibody-induced translational movement in the plane of the membrane. A similar pattern was observed for fibronectin (LETS protein, fibroblast surface antigen). These macromolecules were lost when fibroblasts were dissociated and examined in suspension cultures and were not regained until after the cells were replated. On the basis of the morphological findings, and in view of the likelihood of an interaction between fibronectin and collagen, we propose that these that these proteins form a meshwork on the cell surface. This external protein meshwork may mediate a number of important cellular functions, including attachment to a substratum and other interactions with the extracellular matrix.