The work of Bowden and his collaborators on the boundary lubrication of metals by fatty acids has shown that for efficient lubrication chemical reaction and soap formation must occur. More work has suggested that more than an adsorbed monolayer of soap on each of the sliding surfaces is required to produce a low coefficient of friction. An investigation has been made of the lubrication of several metals by a series of fatty acids. The friction results show that reaction and soap formation occur and that more than a monolayer of soap on each sliding surface is required for good lubrication