A consistent theory of plasma soliton interaction with resonant particles is developed. A simple derivation of a perturbed K.orteweg-de Vries equation with the interaction term is presented. It is shown how the known limit cases (such as Ott-Sudan's, etc.) can be derived from the general equations and what their regions of applicability are. Some effects caused by the soliton-particle interaction (amplitude change-rate, tail formation, etc.) are analyzed by means of a recently developed perturbation method. The analytical results are compared with a direct numerical integration of the perturbed Korteweg-de Vries equation. Laboratory measurements carried out in a strongly magnetized, plasma-filled waveguide and results from particle simulation are interpreted in terms of the analytical results. © 1980 American Institute of Physics.