When designing complex membrane processes, different aspects have to be considered. While fundamental questions are addressed in the laboratory phase, the real conditions in the technical process can only be investigated in the course of a complex and extensive pilot phase. To assure a fast, efficient and cost-effective layout, modern and flexible laboratory membrane test units are necessary that can reproduce operational conditions even in the laboratory with small test quantities. The requirements for modern laboratory membrane test units, the design and the procedure for the laboratory tests are presented and illustrated using the recovery of process water during glycerine production as an example.