Measurements of friction and wear were made on PTFE and polyacetal incorporating glass and carbon fibers. Glass and steel were used as counterface materials. The friction of filled PTFE was generally lower than that of filled polyacetal. The fibers greatly reduced the friction of polyacetal, carbon fibers being more effective in friction reduction than glass fibers. Carbon fiber-filled polyacetal displayed a much lower wear rate than glass fiber-filled polyacetal. The wear rate on glass of fiber-filled polyacetal at lower speeds was much greater than that of unfilled polyacetal. Glass fiber-filled polyacetal also exhibited a greater wear rate on steel than unfilled polyacetal. However, the wear reducing action of both fibers was remarkable in filled polyacetal at high speeds on glass. The frictional surface became fiber rich. Hypotheses for the mechanism of formation of fiber rich surfaces, and the mechanisms of wear increasing and reducing action of the fibers, are discussed.