The motion of a charged particle in a circularly polarized electromagnetic wave and a homogeneous, constant magnetic field is investigated. The exact solution of the non-relativistic equations of motion is given in integral form. The solution of an approximate equation with terms of the order of υ/c neglected is discussed in detail. In the case of cyclotron resonance the time necessary for a deuteron to attain the energy T = 109 °K is expressed by the formula ι = 2.4 × 10−6/H0 (sec).The motion of plasma when its own electromagnetic field is taken into account it then investigated. The method of solution for the non-stationary motion of a plasma, presented in Ref. 1 is applied.If the frequency of an external electromagnetic field is greater than the cyclotron frequency for ions, the mean energy per ion (in degrees Kelvin) transferred directly to the ionic part of the plasma increases with time as follows T = eH02H3(0)ι/3 k McN0.This means, for example, that in an axial field H3(0) = 10 000 G and a circularly polarized field of amplitude H0 = 100 G, the time necessary for plasma to achieve the energy corresponding to 109 °K (disregarding losses) is 4.3 × 10−4 sec.