It is shown that a chemical exchange model can reproduce nuclear magnetic relaxation caused by diffusion of water molecules near strongly magnetized particles. The agreement is based on the similarity (but not equivalence) of the respective “visit-limiting” mechanisms in the echo-limited regime. The model leads to a single equation that predicts relaxation behavior in both the motional-averaging and visit-limited regimes. When combined with the static-dephasing regime equation, the result is a simple theory (for spheres) that covers the entire range of diffusion times. Magn Reson Med 47:388–391, 2002. Published 2002 Wiley-Liss, Inc.