Contact adhesion and sliding friction of octadecylamine and silane molecules adsorbed on silica fibre were measured with orthogonally crossed silica fibres using an electronic microbalance. Interfacial shear strengths, tau, as a function of contact pressure, P, between organic films were deduced from the adhesional model of friction using the measured frictional force and the calculated real area of contact. The pressure dependence of the interfacial shear strength was then interpreted in terms of the molecular interaction of adsorbates with solvent and the surface energetics of molecules adsorbed on the silica fibre.