Observations from sensors on the IMP 8 and ISEE 3 spacecraft have been used to study the characteristics of interplanetary shock-associated energetic particle events. In the energy range above 200 keV, we find that large ambient proton flux levels from the parent solar flare are associated with hard spectra downstream from the shock. At ~40 keV/nucl, immediately behind the shock fronts the He/H flux ratio of shock-accelerated particles is strongly correlated with the upstream He/H density ratio in the solar wind, but not with the flare He/H ratio. The correlation between the shock accelerated He/H and the solar wind He/H ratios is linear. Immediately downstream from the shock front, the energy spectral indices of protons and alpha particles are equal. Measured at the same energy/nucleon, the (46 keV/nucl) energetic particle He/H ratio is the same as the solar wind He/H ratio uppstream from the shock, while at the same energy/charge, the energetic particle He/H ratio shows an enhancement by a factor of 4 to 5 compared with the solar wind. Many of these findings are consistent with a first-order Fermi acceleration origin of the energetic particles. Suprathermal particles from the shock-heated solar wind appear to be the primary seed population of the shock-associated energetic particles near ~40 keV/nucl. However, for that accelerated energetic particles of energies in the range above 200 keV, a more energetic seed population appears to be important.