Using a pin-on-disk apparatus, experiments were carried out to determine the wear coefficients of the nine elemental metals which form little or no oxide in air (ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold) when sliding against each other. The tests mere unlubricated in air at room temperature. It was found that the lowest wear coefficients involved hexagonal metals and incompatible metal pairs. For pairs of metals differing in hardness, the ratio of wear volumes of the two metals was the inverse of the ratio of penetration hardness. In general, the scatter of wear volumes was far lower than that observed in previous tests using oxide-forming metals, in which cases the oxide layers were perturbing factors. The test results suggest that the current practice of using alloys based on gold, platinum and palladium in sliding electric contacts is not optimum, and that combinations involving rhodium and ruthenium deserve consideration.Presented as an American Society of Lubrication Engineers paper at the ALSE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978