The diffusion of water in carbon and glass reinforced epoxies was investigated over a range of humidities from about 33 to 97%, by immersion, and at temperatures in the range 23 to 100°C. (The water absorption properties of the resins themselves were described in the first paper of the series.) The composites obeyed Fick's law, that is, water absorbed was determined by the square root of the immersion time during the initial absorption. The volume of water absorbed at equilibrium by the composites was usually determined by the polymer matrix volume. Where there were exceptions to this, there was evidence of water being concentrated at the fiber-matrix interface. The results otherwise indicated that there was a linear relation between water absorbed at the interface and the temperature. Diffusivities decreased linearly with the square root of fiber volume fraction for both carbon and glass fibers, and under all conditions tested. The fibers thus appeared to act as barriers to diffusion. However, there was strong evidence that these composites had regions with enhanced diffusivity.