The variation in the surface topographical parameters for the case of sliding between high density polyethylene and poly(vinyl chloride) pin ends and a steel disk periphery was investigated. Sliding surface profile ordinate data were obtained at 2μm intervals using a data acquisition system, both along and perpendicular to the direction of sliding. A number of surface roughness parameters, viz., the r.m.s. and c.l.a. roughness, the slope, density, and radius of curvature of asperities, the standard deviation and distribution of profile ordinates, slopes, radii of curvatures and heights of asperities were calculated using a Fortran IV computer program. The analysis showed that the surface parameters undergo a marked variation during the early part of sliding, but the variation is statistically insignificant during the later part. It was found that the standard deviation of peak heights can be approximated by the r.m.s. surface roughness.