The authors consider echo effects in a plasma that are due to the non-damping nature of the distribution function oscillations which occur under the influence of time-displaced perturbations. The case of two external perturbations is considered. The high-frequency and low-frequency echo oscillations occurring in a plasma under the influence of external charges are investigated; in particular, echo effects associated with oscillation conversion are considered. It is shown that one can have in a plasma echo phenomena associated with oscillations whose dispersion is determined by the nature of external perturbations of the distribution function. Echo oscillations in a non-equilibrium plasma in which there is directed particle motion are considered. It is shown that re-excitation of strongly damping short-wave oscillations in a plasma may be accompanied by long-wave echo oscillations leading to plasma instability.