Experiments have been carried out for adiabatic concurrent gas-liquid flow of nitrogen and water through two corrugated test sections. This study examines flow patterns as the gas fluxes are increased. At low gas fluxes two main patterns have been observed: stratified flow for low liquid fluxes and bubble flow for greater ones. The mean wall shear stress of the two-phase flow has been measured with the electrochemical method (polarography); its analysis reveals the flow structure modification from monophasic to two-phase flow. (C) 2000 Elsevier Science Ltd. All rights reserved.