A model encompassing plasma transport and energy processes is applied to Neptune's magnetosphere. Starting with profiles of the neutral densities and the electron temperature, the model calculates the plasma density and ion temperature profiles. Good agreement between model results and observations is obtained for a neutral source of 5¿1025 s-1 if the diffusion coefficient is 10-8L3RN2s-1, plasma is lost at a rate 1/3 that of the strong diffusion rate, and plasma sub-corotates in the region outside Triton. ¿ American Geophysical Union 1993