This paper examines the general problem in which a system "jumps" between two potential wells. The conditions governing the "rate equation" are applied to a model in which an extended dislocation jumps about a pinning agent. The environment seen by the model under a cyclic stress of amplitude σ0 and at temperature T can be represented by a point (σ0, T) on an activation diagram. Regions of different behavior of the model can also be represented on the diagram.