The term Electrokinetic Sonic Amplitude, or ESA refers to the generation of ultrasound by the application of MHz electric fields. ESA measurements are frequently used in colloid science to determine the zeta potential and particle size in concentrated sols, and commercial devices have been developed for this purpose (R.W. O'Brien, D.W. Cannon, W.N. Rowlands, J. Colloid Interface Sci. 173 (1995) 406). The aim of these two papers is to explore the possibility of using ESA measurements to determine membrane properties such as zeta potential and pore size. In this paper we describe a procedure for using the ZetaProbe(1) to measure the ESA of a filtration membrane, and we present measurements for some small-pore membranes. By using the theory for membrane ESA, which is presented in part II of this paper, we have been able to extract precise zeta potentials, but we could not get information about pore size. This is not a limitation of the ESA method but is a limitation due to our frequency range, for to get pore size distributions for these membranes from the ESA it is necessary to work at frequencies omega for which the ratio omega a(2)/v is not small, where a is the pore radius and v is the kinematic viscosity of the solvent; such frequencies lie above the range of our current device. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.