The effect of a small proportion of a polar additive in paraffinic base oils has been studied. The experimental test device is a disk machine. The traction is measured in different lubrication regimes. First of all, as a reference, it was found that in the real EHD regime (Λ > 2), no friction-reduction effect occurs. In contrast, where a thin-film situation exists (Λ < 2), an important friction modification appears. Evidence is given that this effect is related to the presence of an absorbed layer on metal surfaces. These results are also discussed in terms of structural properties of the solution.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983