The transmission of CO2 laser radiation by polycrystalline AgClxBr1-x fibres was measured during cyclic bending of the fibres. These fibres are useful as flexible infrared optical fibres, and it is important to know their fatigue strain limit for applications which require many bending cycles. The investigation was performed in the regime of forced bending vibration. The fibres were found to transmit without significant deterioration after more than 10(7) cycles. Fatigue strain limit values, based on 10(7) bending cycles, are in the range of 0.05%-0.30%. These values were found to depend on the composition and to exhibit a maximum for the AgCl0.5Br0.5 composition. This dependence on composition has been explained by a theoretical model.