Pulsed-gradient spin-echo (PGSE) NMR is a powerful technique that can directly measure the self-diffusion coefficient of molecules in a variety of environments. PGSE NMR can typically measure motions of at least similar to 10(15) molecules in the milliseconds-to-seconds time scale. Here we demonstrate for the first time that through the use of a unique miniature resonator and powerful and rapid gradient sources, electron spin resonance (ESR) can also be employed to measure diffusion in liquid state. The PGSE ESR method, which operates at the microseconds time scale with much higher molecular sensitivity, can complement and enhance the current capabilities of NMR. (c) 2008 Elsevier B.V. All rights reserved.