An experimental technique which measures the forces of interaction between lipid bilayers with and without a surface layer of protein is described. Results are given for the forces between dilaurylphosphatidylcholine (DLPC) bilayers; cerebroside sulphate–cholesterol (CES/CHOL) bilayers (both 60/40 and 80/20 mol %); and Myelin basic protein (MBP) adsorbed on 60/40 mol % CES/CHOL bilayers, and directly on mica. The results obtained for DLPC showed a short-range attraction, whilst for both charged lipid systems a long-range double-layer repulsion was observed. At 11 nm this was replaced by a much steeper repulsive force. No attraction between these bilayers was observed. However, when the myelin basic protein was associated with the CES/CHOL, a strong attractive force was measured.