This study considers the sliding friction in reciprocating motion, plane on plane and dry contact between very smooth surface of a steel slider and three engineering thermoplastics : ultrahigh-molecular weight polyethylene, polyoxymethylene and PA 66. Dynamic coefficients of friction were accurately measured at ranges of apparent contact pressure varying between 25 and 800 kPa and sliding speed between 0.01 and 0.1 m s(-1), using plastic samples whose surface roughness was fully characterized. The frictional behaviours in reciprocating motion were found to be equivalent to those reported by previous workers who have tested similar materials in continuous motion. These results were used in the evaluation of non-Hertzian elastic contact stresses considering a simplified model of cylindrical tips of asperities of plastic materials making contact with a polished and hard semi-infinite plane. Fatigue failure analysis was conducted and the combination of the Marin equation a nd the Soderberg fatigue failure criterion used to evaluate the factor of safety. The results of this analysis were summarized graphically in the form of load-frequency capabilities that represent the onset of excessive fatigue wear for each plastic material. Scanning electron microscopy observations of worn plastic samples enabled the illustration of the mechanism of formation of wear particles in the case of the present tribological system. The results of the qualitative evaluation of the amount of wear showed the importance of the decrease in normal load in order to increase the factor of safety, despite the increase in the coefficient of friction so induced for most thermoplastics.