Abstract The electron distribution function is calculated explicitly for a weakly ionized plasma under the action of an alternating electric field E = {0 , 0 , Eoz cos ω t} and a circularly polarized magnetic field BR = Bc{cos ωB t, sin ωB t, 0} rotating perpendicular to the a.c. field. Furthermore, a constant magnetic field B0 = {0, 0, B0} is taken into account. The isotropic part f0 of the electron distribution function which contains, in special cases, well-known standard distributions (distributions of Druyvensteyn, Davydov, Margenau, Allis, Fain, Gurevic) shows a resonance behaviour if the frequencies ω, ωc = (q/m) Bc , ω0 = (q/m) B0 , and ωB satisfy the relation ω= This can be understood as a generalized cyclotron resonance phenomenon.