It is generally agreed that plasma in the magnetosphere of Neptune is produced primarily in the vicinity of the orbit of Triton, near and beyond 14 RN, and is then transported inwards toward Neptune. The observed temperature profiles of protons and nitrogen ions, however, show an initial decrease with decreasing distance from Neptune, the expected increase from adiabatic compression not setting in until distances below 8 RN have been reached. We propose that cooling produced by collisions with atoms of a neutral hydrogen cloud that extends inward to 8 RN may explain this behavior, at least for protons. Inclusion of inelastic scattering in addition to the more commonly invoked charge exchange makes cooling sufficiently effective so that the observed temperatures may be accounted for with plausible values of neutral hydrogen density. ¿ American Geophysical Union 1995.