Water is scarce in the Middle East, and irrigation consumes 90% of this resource. Efforts to schedule irrigations for efficient water use are hampered by the lack of regionally specific data on crop water use. A weighing lysimeter for crop water use determination was constructed in the Jordan Valley, which has been described as a natural greenhouse and which serves as a year-round source of fresh vegetables and fruits for the region and for export to Europe. The lysimeter is 3 by 2.5 m in surface area and 2.5-m deep, masses 40 Mg, and measures crop water use with a calibrated accuracy of 0.05 mm. Design considerations and details are given. Data from the lysimeter will be used in the Middle Eastern Regional Irrigation Management Information Systems project (http://www.merimis.org/) to provide reliable information for irrigation scheduling to farmers from Jordan, Israel and the Palestine Authority.