We present initial measurements of the three-dimensional magnetosheath plasma ion flow and spectrum over the energy range of 200 eV to 2 MeV. These observations are from two magnetosheath traversals, one each on the dawn (December 19, 1977) and dusk (July 7, 1978) flanks of the magnetosphere. Data are from three-dimensional plasma and energetic ion observations from the ISEE 1 satellite. The data show the continuous presence of a high-energy (>5 keV) tail in the magnetosheath ion population during these two traversals. Comparisons with plasma sheet data lead us to conclude that for the two cases studied the magnetosheath plasma often has at least two major components, the shocked solar wind seen at energies ≲5 keV and magnetospheric (plasma sheet) particles seen at energies >5 keV. At times, however, magnetosheath spectra are observed that indicate the presence of only a shocked solar wind component that includes a high-energy tail possibly produced either by ambient energetic solar particles or by acceleration processes at the bow shock. The shocked solar wind component at energies ≲5 keV behaves independently of the magnetic field direction, indicating that the frozen-in field approximation applies. The high-energy tail at energies >5 keV is highly modulated by the magnetic field. In the strongly varying magnetic field case of December 19, 1977, energetic ion transport in the plasma rest frame occurs by diffusive processes which result in an isotropic energetic ion distribution in that frame. The imposition of the plasma bulk velocity on this distribution results in the energetic ion anisotropies observed in the satellite frame. In the much more ordered field of July 7, 1978, energetic ion transport occurs via single-particle motion along magnetic flux tubes in the plasma rest frame. The transport of flux tubes past the satellite as they change direction and connect/disconnect to remote particle sources causes the variations in energetic ion intensities and anisotropies observed in the satellite frame. ¿ American Geophysical Union 1988