We consider the energy loss by a fast test ion in a plasma and tabulate numerical results for the corrections to the usual dominant "InA" term in the loss rate (for all values of the ratio between test ion and plasma electron thermal speeds). As a preliminary consideration, we present a derivation of the Fokker-Planck equation which treats both close collisions and cooperative plasma effects fully; the resulting equation is not new but the derivation is novel and has simplicities which facilitate calculation.