Glycophorin was incorporated into large unilamellar vesicles and the bilayer permeability was measured as a function of the lipid composition. In agreement with previous data (Van der Steen, A.T.M., De Kruijff, B. and De Gier, J. (1982) Biochim. Biophys. Acta 691, 13-23) it was found that glycophorin greatly increased the bilayer permeability of DOPC vesicles. This effect was observed for a large variety of phosphatidylcholines, differing in their fatty acid composition and homogeneity. In sharp contrast, it was observed that variations in the polar headgroups by incorporation of DOPE, DOPS and, to a lesser extent, cholesterol, into the DOPC/glycophorin vesicles restored the barrier function. These results are compared to the size of the particles, revealed by freeze-fracture electron microscopy on the glycophorin-containing bilayer and are discussed in the light of various types of lipid-protein interactions and protein aggregation state.