A hydrophilic, positively charged, durable coating has been developed for capillary electrophoresis of macromolecules. Polyethyleneimine is adsorbed to the inner wall of fused silica capillaries and the adsorbed coating cross-linked into a stable layer. Capillaries of polyethyleneimine-coated silica gave unique separations owing to the reversal of electro-osmotic flow caused by the positively charged coating. The resulting coating was stable from pH 2-12 and could be used over a wide pH range without substantial change in electro-osmotic flow. High-molecular-weight polymers were needed to give thick coatings which mask silanol groups on the wall. Proteins were resolved quickly and efficiently with good recovery using capillaries of 50 cm in length.