An experimental setup combining a swollen-polymer test surface and an electronic speckle-pattern interferometer (ESPI) to measure mass transfer in situ in wind tunnels is presented. The principles of the measurement technique are reviewed, and the problems posed by tunnel noise and vibration are discussed. In the present installation (for a tunnel with a 260-kW fan and motor), the ESPI is surrounded with antivibration pads and mounted on an optical table supported on a slate sheet over inflated inner tubes, and the system stiffness is adjusted until the interferograms remain clear with the motor running. Preliminary results obtained with this setup have been reported by Butcher et al. (1984).