We present the experimental observation of periodic quasi-equilibria in solid-state NMR. We observe these states in ordinary cross-polarization magic-angle spinning experiments on powder samples of ferrocene and alanine, and we compare our results with numerical simulations. The spin dynamics are explained by considering the coupling to the lattice as a coherent broadening of the eigenlevels of the Hamiltonian. (C) 1999 Elsevier Science B.V. All rights reserved.