This paper introduces a novel optimal design strategy for membrane separation systems. This strategy is characterised by two main features: firstly, detailed models are used. This is essential if sub-optimal and inaccurate solutions are to be avoided. Secondly, an optimisation technique based on genetic algorithms is implemented. The feasibility of the optimal design strategy is investigated using a pervaporation case study. To this end, an existing pervaporation plant is evaluated and a significantly improved design is found. (C) 2003 Elsevier Ltd. All rights reserved.