The plasma investigation made use of two Faraday-cup detectors, one pointed along the earth-spacecraft line and one at right angles to this line. The earth-pointing detector determined the macroscopic properties of the plasma ions, obtaining accurate values of their velocity, density, and pressure. Three sequential energy scans were employed with (delta E)/E equal to 20, 7.2, and 1.8%, allowing a coverage from subsonic to highly supersonic flow. The side-looking Faraday cup measured electrons in the energy range from 5 eV to 1 keV. The plasma parameters are obtained by finding the best fit of a convected isotropic Maxwellian distribution to the data. One sigma errors are typically less than 0.5% in the speed and VR, less than 5% for the density and thermal speed, and vary greatly for VT and VN. Sampling times range from 12 to 192 sec., with sampling generally more frequent early in the mission. One hour averages were produced from these samples. The velocity components are given in the RTN coordinate system, where R is radially outward, T is in a plane parallel to the solar equatorial plane and positive in the direction of solar rotation, and N completes a right-handed system.