We show that the optical indicator technique used to visualize fast hydrogen migration in thin metal films can also be applied in an electrochemical set-up. Lateral diffusion of hydrogen in a vanadium film under a masking layer could be monitored from the optical change of an yttrium switchable mirror, which served as an indicator for the diffusion front. An electrochemical loading experiment provides a precise measure of the total hydrogen content of the sample. Optical reflectance measurements allow the determination of the diffusion coefficient of hydrogen. Additionally, the electrochemical set-up was used to measure a room-temperature solubility isotherm of the film under investigation. The observed miscibility gap was smaller than that of the bulk metal. (C) 2003 Elsevier B.V. All rights reserved.