The paper is concerned with surface roughness analysis as a means of investigating lubricant action in cutting. An experimental setup involving a high-resolution signal analyzer has been used to obtain power spectrum characteristics, as well as conventional surface roughness parameters, of surfaces machined using different work materials and cutting fluids. Across the lay, conventional roughness parameters are dominated by the feed marks, and discrimination between different lubricating conditions is difficult. Frequency analysis, on the other hand, permits one to isolate the feed component, thus making it possible to ascertain the effect of lubrication at other wavelengths. The lubricating action is even more pronounced when measurements are performed in the machining direction, though a larger scatter among the results is experienced here. The averaged power spectrum ratios of surface roughness measured in the direction of cutting are used to describe the lubricating action.Presented at the 37th Annual Meeting in Cincinnati, Ohio May 10–13, 1982.