The different configurations of on-line dialysis in flow injection analysis is reviewed. A short historical background is given, with reference to the incorporation of on-line dialysers in nonsegmented, continuous-flow systems, mainly in the late 1960s, and the origination of flow injection systems, in the mid to late 1970s. The basic principles of dialysis are briefly given, and dialyser design and membrane materials are discussed briefly. Development of the theoretical principles is briefly outlined in a theoretical background The dialysis process is discussed in terms of the functioning of the dialysis unit in a prevalve or in-valve position, as part of the manifold or detector, or as a microdialysis unit in a intracerebral in-line position.