We examine data on particle events resulting events resulting from three solar flares, two of which generated interplanetary shocks, to determine the effect of the shocks on the population of protons at energies > 30 MeV. In both cases, the arrival of the shock marks the start of the decay phase of the particle event, and changes in particle anisotropies are related to features in the shock structure. We conclude that each shock is a source of protons with energies > 30 MeV, which propagate along the interplanetary magnetic field lines and are observed at large distance (1 AU) away from the shock. A model in which these protons are accelerated by the shocks rather than being stored in or contained behind the shocks is shown to be consistent with observations.