Thermally activated dynamics of double-well systems is reexamined as a possible mechanism of electron spin-lattice relaxation (SLR) of paramagnetic centers in glasses. Using the soft-potential model, we have found that this mechanism can explain a nearly quadratic temperature dependence of the SLR rate in various amorphous materials over the temperature range 1-100 K. This mechanism is expected to be operative over this temperature range, as opposed to the phonon-induced tunneling of two-level systems, which is usually considered as the mechanism responsible for this behavior. (C) 2011 Elsevier B.V. All rights reserved.