A study is made of the role of ergodic relationships (related to the Hamiltonian of the zeroth
approximation $\mathscr H_0$ ) in the construction of kinetics when there are alternating external fields.The integral equations obtained for the density matrix determine the non-Markov nature of the evolution of a system in a high-frequency external field. In the low-density approximation kinetic equations are obtained for the Wigner distr ibution function with a collision integral that is nonlocal in the time. A study is made of the relationship between the questions considered in this paper and the nonequilibrium statistical operator method of Zubarev and Kalashnikov.