AbstractVelocity distribution functions and the reactivity are calculated for D–T fusion plasma with spin-polarized fuel. The distribution functions are classified by spin states. Binary collisions and the resonance with waves are taken into account as depolarization mechanisms in plasmas. Spin–orbit interactions are shown to have no deleterious effect. However, lower hybrid heating and current drive using GHz waves resonant with the spin precession frequency are found to cause complete depolarization, when δB/B0 (the ratio of the amplitude of the fluctuating magnetic field to the external field) exceeds 10−5. Thus electron heating may increase the retention of polarization. Other depolarization mechanisms in plasmas will be also discussed.