The distribution functions of interstellar pick-up hydrogen and helium exhibit fluctuations which are correlated. An analysis of these fluctuations reveals that they may be the result of variations in, and provide additional evidence for, large mean free paths for these low rigidity particles. An analysis of the properties of the distribution function of pick-up hydrogen reveals that these particles do suffer considerable adiabatic cooling, and that the likely cause for the long mean free path is the inability of the particles to scatter through 90¿ pitch angle.¿ 1997 American Geophysical Union