A model system for retinal adhesion, consisting of interacting bovine pigment, epithelium (PE) cells and photoreceptor outer segments, was utilized to examine any adhesive role of the interphotoreceptor matrix. PE cells were dissociated by trypsin treatment of the eyecup, and were allowed to replenish their surface proteins as single cells in spinner culture. They were then placed into short-term, slowly rotating suspension cultures, where their rapid aggregation as a function of time could be studied. Outer segments exhibited no tendency to interact with one another, or with PE cells, in suspension culture. Extracellular interphotoreceptor matrix from adult bovine eyes was isolated by rinsing the apposing surfaces of neural retina and PE. When this matrix material was added to the cell suspension cultures, adhesion between PE cells and outer segments in mixed cultures was not enhances. However, PE reaggregation itself appeared to be augmented. The principal matrix glycoprotein, obtained by concanavalin A affinity chromatography, displayed adhesive properties similar to those of the interphotoreceptor matrix. Thus, under the conditions of these in vitro experiments, no evidence could be obtained that either cell surface molecules or interphotoreceptor matrix plays a role in retinal adhesion.