In the present work, an experimental investigation is presented which is focused on the pressure drop along the heated as well as the unheated zone of a flow channel. The experiments were performed by using a 16 mm stainless steel ID tube with a 350 nun heated length followed by a 500 mm unheated extension downstream. Pressure drops and pressure distribution were measured along the flow channel, with water, at mass flow velocities of 6342-9513 kg/m(2) s and at heat fluxes of 3.37-4.1 MW/m(2). The whole experiments were conducted near atmospheric pressure by keeping the outlet of the flow channel open to the atmospheric pressure. The experimental results show a reduction of the pressure at the outlet of the heated zone at the onset of significant void (OSV) conditions, caused by the increasing of the average velocity at that zone. That reduction of the pressure, at the outlet of the heated zone, decreases as the inlet (and also the outlet) temperature increases, due to the increasing of the length of the two phase flow at the unheated zone. That phenomenon is backed by photographing the flow in the unheated zone. (c) 2006 Elsevier Ltd. All rights reserved.