We address the problem of measuring accurately and as quickly as possible a self-diffusion coefficient by the so-called pulsed gradient stimulated echo experiment or, equivalently, by using a sequence involving radio-frequency field gradients. The discussion deals with the smallest diffusion coefficient which can be measured with a reasonable accuracy, possibly taking into account the values of longitudinal and transverse relaxation times along with the nature of gradients. It is shown theoretically and experimentally that the diffusion coefficient can be measured accurately via only two experiments provided that the ratio of the signal amplitudes lies in the range 0.2-0.6. (c) 2005 Elsevier B.V. All rights reserved.