The macrophysics of a single-fluid plasma at a hydrodynamic shock is characterized completely by the three Rankine-Hugoniot conditions expressing conservation of particles, momentum flux, and energy flux across the shock. In a multifluid plasma containing an arbitrary number of ion species and electrons the Rankine-Hugoniot conditions still characterize the behavior of the bulk plasma but not the properties of individual fluid constituents. Conservation laws for individual particle species are derived for parallel collisionless shocks. The shocks are assumed to be nonturbulent; i.e., the particles interact only via the electrostatic field. Given the plasma parameters upstream, the downstream solutions form a single-parameter family; the free parameter can be taken to be the electrostatic potential jump across the shock. ¿ American Geophysical Union 1991