We present a new method of controlling protein adsorption during capillary electrophoresis which involves placement of a thermally treated monolayer of adsorbed fibrinogen on the internal surface of the fused silica capillary. The thermal treatment is shown to render the adsorbed layer stable to an applied electric field. In contrast, an adsorbed layer not receiving thermal treatment will exhibit steady desorption when exposed to an electric field. Protein coated capillaries exhibit a surface potential and an electro-osmotic mobility that are (i) 30% smaller that those of bare capillaries and (ii) stable over several measurements. Protein coated capillaries will likely be useful in bioseparations utilizing proteins.