Surface roughness affects friction, but it is not clear what surface roughness characteristics are better correlated with friction. The average ofthe maximum height above the meanlinein eachcut-o!length(R1.)and the arithmetical average of surface slope(*!) had the highest correlation with dynamic friction coe$cient in a previous study. The previous study was expanded to two di!erent footwear materials and four di!erent contaminants on a porcelain tile in the current investigation. The results showed that dynamic frictiondecreased as the interface speed and glycerol content in the contaminant were increased due to the hydrodynamiclubrication e!ect. *! had the highest correlation with friction for most of the test conditions with neolite. For Four S rubber, friction coe$cient appearedtohavethehighestcorrelationwiththeparametersrelatedtothesurfacevoidvolumeat30%glycerolcontent,relatedtothe surfaceslope at 70 and 85% glycerol contents,and related to the peak to valleydistance at 99% glycerolcontent. A good indicatorof surface slip resistance probably should consist of the surface parameters representing the surface slope, the surface void volume and thesurfacepeak-to-valleydistancewiththecoe$cientsdeterminedbythesystemparameters. ( 2001ElsevierScienceLtd.Allrights reserved