This paper reports the fatigue behavior of an injection molded 40wt% talc-filled polypropylene. The effects of specimen orientation relative to the flow direction, weld line, hole stress concentration and test frequency on the fatigue performance of this material have been considered. The fatigue strength in the flow direction was higher than that normal to the flow direction. However the orientation effect decreased at lower fatigue stress level. The presence of weld line reduced the fatigue strength. On the other hand, the fatigue strength showed very little sensitivity to the presence of hole stress concentration. The failure mode in fatigue was influenced by the test frequency. When the test frequency was less than or equal to 2 Hz, the failure mode of the talc-filled polypropylene was due to fatigue and the fatigue life increased with frequency. However, when the test frequency was greater than or equal to 5 Hz, the failure of the talc-filled polypropylene was due to thermal softening and the fatigue life did not appear to be influenced much by the frequency. (c) 2005 Society of Plastics Engineers.