The build-up of particulate cake layers on porous surfaces such as those arising in cross flow microfiltration has been investigated using a new mode of operation of the fluid dynamic gauging (FOG) technique reported by Chew et al. [1]. FDG was used to track, in situ and in real time, the build-up of a filter cake during microfiltration of a suspension using pressure mode FOG, which is shown to give comparable results to conventional FDG (where the amount of liquid withdrawn from the system may vary). Validations of pressure mode FOG are reported, alongside a short demonstration study using mixed cellulose ester membranes and glass ballotini suspensions. Measurements of changes in permeate flux allowed the cake resistance to be calculated and the thickness of the cake estimated: these results gave good agreement with the FDG measurements. Computational fluid dynamics (CFD) simulations of the flow in the duct, in the gauge, and across the membrane and were performed to elucidate the flow patterns and stresses imposed on the surface being gauged. The flows were in the laminar or inertial regime, and the simulations gave good agreement with experimental measurements. The scope for using pressure mode FOG for studying fouling and cleaning in membrane modules operating at higher pressures is established. (C) 2010 Elsevier B.V. All rights reserved.