Membrane distillation (MD) is considered a promising technology for desalination applications. Usually, the investigations stated in MD literature cover lab-scale experiments to analyse the technology's potential. This work is focussed on experimental studies on full scale spiral wound MD-modules with a membrane surface area of 5-14m(2). Module technology and module fabrication are introduced, as well as the fully automated performance test facility and the characterisation procedures. Statements regarding module fabrication quality are given by a comparison of a four module production charge. The experimental results consider module output rate and specific energy consumption for a broad variety of module operation points. The interaction of feed flow rate, temperature levels, feed water salinity and geometrical module design parameters are quantified and discussed. Special attention is given to the influence of salinity on module performance. The salt rejection rate throughout all experiments is very high and almost independent from any studied operational parameters. Finally, a preliminary approach shows the feasibility of high purity distillate production with the spiral wound modules. In a emulated double stage process the distillate conductivity was dropped down to 0.19 mu S/cm. (C) 2011 Elsevier B.V. All rights reserved.