The radial profiles of local void fraction and velocities of both phases were measured in subcooled boiling flow of water in a vertical concentric annulus with a heated inner tube. A two-conductivity probe technique was used for the measurements of local void fraction and vapor velocity and a Pitot tube method was applied to measure the local liquid velocity. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling. Based on the measurements, the influence of such flow conditions on the distributions of local flow parameters was investigated. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow in the computer code CFX-4.2. (C) 2002 Published by Elsevier Science Ltd.