Sliding friction between an 1/8 in. spherical steel rider and a gold-plated steel flat was measured for various loads (200–2000 gm), gold film thicknesses (0.1–10 μ) and steel combinations (440C and 52100). Coefficient of friction recorded in each run for 100 traverses was found to be most sensitive to the rider material (0.1–0.3 with 440C rider and 0.1–0.6 with 52100 rider, as compared to 0.6–0.7 for unlubricated steel). With a 52100 rider, as the number of traverses increase three distinct types of frictional behaviors were found: (A) slowly decreasing, (B) rapidly decreasing, and (C) increasing (sometimes a minimum was first reached). Theoretical coefficient of friction (0.1) was only observed with 'Type B' results. With a chromium rich 440C rider, friction was always low presumably due to its low affinity to gold.Presented as an American Society of Lubrication Engineers Paper at the Lubrication Conference held in Minneapolis, Minnesota, October 18–20, 1966.