Abstract Even though very important advances have been made, present membrane technology does not seem to have lived up to early expectations. In spite of significant improvements in membrane properties and module design, they have not solved the problems of membrane fouling and secondary membrane formation. Because this phenomenon controls the average flux and rejection regardless of the original intrinsic membrane properties, the fouling problem is probably the most serious one. Every improvement in this direction is of significant importance to the industrial implementation of membrane technology. Carrying through industrial applications of UF and RO requires close technical and financial co-operation between the manufacturer and the customer, and a high level of expert knowledge on the part of the field salesmen. Better information about membrane technology and its features is needed, as is knowledge about other processes to be used in conjunction with it. The biggest potential market for membranes is the generation of pure water and the treatment of effluents. The first of these has already been quite successfully penetrated, particularly with regard to brackish water demineralization. A breakthrough in the effluent treatment market requires better fouling control methods. For valueless liquids, the only incentive will be valid environmental legislation. To make membrane technology attractive to industry will otherwise require the recovery of a valuable component.