Boron removal using new generation RU membranes from several leading manufacturers under a second-pass configuration and without pH adjustment was studied. The study was conducted using seawater from the Arabian Gulf (higher salinity and temperatures than average seawater). Membranes from several manufacturers were tested under similar operational conditions and the same feed water source. It was found that significant boron rejections, as high as 96%, were successfully achieved, using readily-available commercial RU membranes under a two-pass configuration and without any pH adjustment. Moreover, single-pass configurations exhibited high salt and boron rejection results reaching 99% and 91%, respectively. First pass permeates had boron levels below 1.4 ppm, which are adequate to comply with the new WHO guidelines (2.4 ppm) and those of other countries such as Australia, Canada, and UAE, whose boron guideline thresholds are above 1.4 ppm. The paper also assesses the influence of several operational parameters such as feed water salinity, flow velocity, temperature and feed pressure in second pass on boron removal in this process. It was found that higher boron removals were obtained with higher feed velocity, higher second-pass pressures, and lower feed temperatures. (C) 2012 Elsevier B.V. All rights reserved.