The macroscopic fatigue behaviour has been characterized in terms of stiffness reduction and fatigue-life diagrams. The longitudinal Young's modulus degraded more rapidly for glass-fibre/PP (see Fig. 3), which indicates a higher degree of damage growth and accumulation. The glass-fibre/MA-PP exhibited a `sudden death' behaviour, where the stiffness remained virtually constant until imminent failure. This implies localized small-scale damage, which can be explained by the more effective fibre/matrix bonding through maleic anhydride modification. The fatigue tests for replications and stiffness measurements were performed at a stress amplitude of ∼60% of the ultimate tensile strength (UTS).