Renal cells in culture represent excellent experimental tools to investigate specific physiological and cell biological functions of the nephron [1—6]. However, with the limitations of present cell culture techniques, these in vitro methods still inadequately mimic an ideal renal microenvironment. Renal cell culture is commonly achieved by diluting the isolated nephron cell type in a suitable culture medium. The cells are then transferred to polystyrene tissue culture plates. Most of the cells attach to the impermeable culture plates, where they divide until a more or less confluent monolayer is achieved. If cultures are utilized for transport investigations, filter inserts for improved polar differentiation can be used. Compared to tissue culture plates it is proposed that filters mimic a more physiological situation since they are semipermeable. In many cases they are useful in inducing the cells to establish a polarized epithelial barrier. However, experiments with filter inserts are limited, because only a relatively small number of different filter materials for optimal cell attachment is offered. Finally, the environment within the culture dishes is far from being physiological. 1) The medium remains unexchanged and unstirred over an extended period of time ranging from one to several days. During this period uncontrolled conditions can develop within the cultures. 2) By the same argument, if hormones are introduced to the medium their bioavailability is barely adjustable. The concentration of hormones may be modified by the cells or by the medium in an unknown manner. 3) The questionable attachment of cells in a culture dish, together with the small choice of biocompatible support materials, and the uncertain composition of an unstirred medium are accompanied by a further problem. It is well known from continuous cell lines, and especially from primary cell cultures, that cells lose many of their morphological, physiological and biochemical characteristics as a result of dedifferentiation [1—3]. With the combination of technical limitations of cell culture experiments on the one hand and the problem of dedifferentiation on the other, it would not be surprising if results in vitro do not reflect exactly the conditions in vivo. Therefore the primary intention of this work was to develop a new cell culture system for anchorage-dependent cells in which a kidney-specific situa-