A spin echo is usually expected to exhibit a maximum at a time 2 tau, where tau is the pulse spacing; for high diffusivities in presence of linear gradients, however, a maximum is observed at times root 2 tau. Here we show that in the presence of non- linear gradients a strong departure from the linear case is obtained. For long echo times a plateau for the maximum signal time is reached, thus a diffusion correlation time dependent both on the diffusion coefficient and the gradients strengths can be defined. Results for laser polarized He-3 and Xe-129 are compared with Monte Carlo simulations. (C) 2009 Elsevier B. V. All rights reserved.