A method to reduce the cycle time of the SBR-process by utilising submerged membranes is described. The time necessary for the sedimentation of the activated sludge and the extraction of the clear-water phase takes up a major part of the entire cycle period within the SBR-process. By using membranes it is possible to start the clear-water extraction already during the reaction time. The time needed for the sedimentation of the activated sludge can be dispensed with altogether. The paper presents the initial results of a semi-technical test plant, with particular emphasis on the fact that the running of the SBR-plant did not lead to any problems with fouling or scaling. In cases of high solids contents, the oxygen input was below par; this, however, did not have any unfavourable impact on the nitrification.