CFRP tendons are a potential alternative to steel reinforcement for pre-stressed concrete. This paper discusses particular characteristics pertaining to the behavior of CFRP when exposed to a combination of moisture and stress, conditions typical to that of pre-stressed reinforcement. Previous studies showed that the imposition of stresses on fibre-reinforced polymer strips and plates caused a change in their moisture-uptake behaviour. This is believed to be caused by a change in free volume, with compressive stresses reducing the free volume in the polymer, and tensile stresses increasing the free volume. Micro-cracking within the epoxy matrix and at the fibre-matrix interface could also increase moisture absorption. Therefore, it is hypothesised that the combination of stress and moisture exposure would accelerate any degradation of CFRP tendons. It is important to validate and quantify this degradation, particularly in the case of pre-stressed concrete where the tendons are typically stressed to 60% of their ultimate tensile strength. A series of experiments have been undertaken where flexural stresses are imposed on CFRP tendons immersed in water. The tendons are stressed to a maximum strain of 0%, 20%, 40%, 53% and 74% of the average fracture strain. The results will then be used as the basis for the prediction of uptake rates in tendons subjected to axial tensile stresses and to model the long term interaction between pre-stressed CFRP tendons and concrete.