In order to determine experimentally the wall shear stresses exerted on a wet foam which is flowing in a horizontal square duct, we examined here the use of a totally innovative method in foam flows: the electrochemical method. We showed that it was necessary to determine the film thickness when the latter is less than a certain critical thickness which is numerically estimated. We experimentally measured the film thickness by conductimetry and showed that the electrochemical signal fluctuations rightly reflected the shear stress fluctuations. We can conclude that the wall shear stress is more important between the bubbles than under the bubbles, like inside a capillary. (C) 2003 Elsevier Science Ltd. All rights reserved.