First results from the Ogo-A positive ion spectrometer experiment are presented for the period September 23 through December 10, 1964. Thermal hydrogen and helium ion distributions extend from the lowest observations at 1500 km to an altitude of 30,000 km. The density obtained for H+ at 2000 km is of the order of 103 ions cm−3, and the He+ concentration is 1% of H+ over most of the altitude range. Whereas the concentration and distribution of H+ observed at the lower altitudes is in general agreement with theoretical models, the upper altitude profiles show significant departure from predictions based on diffusive equilibrium theory. Evidence is presented indicating that diffusion of ions is controlled by the geomagnetic field and that the ions are distributed in a beltlike region which exhibits a sharp gradient resulting in a ‘plateau’ at its outer boundary, which is characterized by a reduction in both the H+ and He+ concentrations by a factor of 10 or more. The ion belt is observed to expand and contract over an altitude range of 8000 to 30,000 km in an inverse relationship with the magnetic activity index Ap. There is significant correlation between these results and the knee whistler observations as well as with high-altitude ionization gradients observed from other satellites. Although the data provide some indication of a direct coupling between the lower and upper ionosphere, more data will be required to describe this relationship adequately.