Equations are set up to describe the quasilinear behavior of a collisionless, relativistic plasma immersed in a uniform, homogeneous magnetic field. Use of the adiabatic assumption, together with an approximation to resonant denominators, enables an estimate to be given of the change of the distribution function due to the turbulent waves. In the particular cases of pure electrostatic waves, magneto‐sonic waves, and cyclotron waves, estimates are made of the rate of energy change of resonant particles. It is shown that some modes exhibit resonant diffusion only when relativistic particles are present and for which there is no nonrelativistic counterpart. It is believed that this calculation may be of some interest in situations where relativistic particles play, or are suspected of playing, a major role; for example, the galactic cosmic ray gas and nonthermal radio sources.