The direct steam generation (DSG) in parabolic trough collectors is a promising option for the improvement of the reliable parabolic trough technology for solar thermal electricity generation. The DISS (direct Solar Steam) test facility at the Plataforma Solar de Almeria is a full-scale solar steam generator consisting of parabolic trough collectors, used to investigate the DSG process under real operating conditions. According to theory and results from lab-scale experiments it was expected that the tilt of the absorber tubes can improve the thermohydraulic behavior of the DSG process significantly. Within the DISS project a test campaign has been performed to investigate the influence of tilt. The evaluation of the test data showed, that the horizontal absorber tube guarantees sufficient cooling confirmed by low temperature differences even at very high steam qualities. (C) 2003 Elsevier Ltd. All rights reserved.