Solid glass beads for use in isolating cell membranes were coated with a stable, covalently attached layer of polylysine. The optimal conditions for coating the bead surface were established and the beads were tested by measuring the attachment of human erythrocyte plasma membranes. When compared to other beads, such as those with absorbed polylysine or protamine, none retained red-cell membranes as well as glass beads with covalently linked polylysine.