The effect of non-Maxwellian distributions of field particles on the slowing-down process of charged particles is investigated. Simplifying assumptions are made in two specific cases. It is found that, in the presence of suprathermal electrons, the slowing-down is more efficient at constant mean energy per electron. It is argued that truncated distributions, which occur for very small pellets, do not cause any significant deviation in the microscopic slowing-down.