The wear and friction behaviour of short glass-fibre-reinforced polyamide 66 composites running against each other, unlubricated, in non-conformal, rolling-sliding contact has been investigated. Both a wide range of loads and slip ratios and a range of samples with different fibre concentration and different crystallinity have been examined. Short glass-fibre reinforcement makes the polyamide 66 exhibit unique tribological behaviour. There is a high resistance to wear and friction which results from a significant "self-lubricating" property. A thin film layer exists on the contacting surfaces when two discs run against each other within the range of the test conditions. It is this thin film that plays a dominant role in the "self-lubricating" property of the composite. The formation of the thin film and the life of the composite depend on a complex of interactions between structure, strength and fibre concentration, and the specific conditions of load and slip ratio imposed. Under identical loading conditions, either lower fibre concentration or lower crystallinity cause the thin film to form continuously during the wear process so that the life of the composite may reach 6 x 10(6)-10(7) cycles. It is suggested that the "self-lubricating" property may be used in the working period of engineering components rather than only during the temporary running-in period of machine elements.