In this study, a novel method based on potential-pH response drift measurement was used to determine hydrogen ion diffusivity in pH-glass electrode membrane. The diffusivity of hydrogen ion in pH-glass membrane obtained from this method was 1 x 10(-8) cm(2)/s. Two pH-sensing mechanisms may be identified for the pH-glass electrode based on the diffusion-site-binding model. These are the charge adsorption mechanism for short time domain and the hydrogen ion diffusion mechanism for long time domain. The hydrogen ion diffusion mechanism may be invoked to explain the observed drift in pH-glass electrode. (C) 2003 Elsevier B.V. All rights reserved.