Monte Carlo simulation has been used to model environmental attack of a fibre tow, and suggested that such attack could lead to fatigue-type behaviour under static load conditions. The system was assumed to be fibre dominated with the presence of matrix cracks relaxing stress in the matrix and providing a path for environmental species to reach the fibres. Lifetime under load was related to the fibre-environment reaction rate and distribution of forces from broken fibres. Fatigue exponents ranging from 1.0 to 1.5 were predicted for selected reaction rates at stress levels less than 140 MPa. Simulation results were compared with literature data, and predicted fatigue exponents were substantially lower than those observed experimentally. This result could suggest that fibre-environment chemical reaction was not the sole mechanism operable in experiments. However, it was suggested that a stress dependent reaction rate could be used to improve the correlation between the simulation and experimental results.