The effect of membrane orientation in a centrifugal membrane system (CMS) on the alleviation of fouling of reverse osmosis (RO) and nanofiltration (NF) membranes by colloidal foulants was examined. Colloidal silica fouling of RO membranes is dramatically reduced relative to a conventional reference system for all membrane orientations except (0, 180, 0) in which the centrifugal force is directed towards the active face of the membrane. The fouling of RO membranes by humic acid is not alleviated to the same extent as the silica case except for the (90, 90, 0) orientation that combines a favorable alignment of the centrifugal force along the. membrane face, and a Coriolis force also along the membrane face. The influence of these two factors is also seen in protein fouling of a NF membrane. The critical Bur in NF is significantly enhanced by CMS even though a substantial protein-fouling layer is present on the membrane. Some membrane orientations in the CMS environment can inhibit the onset of a fouling layer and, once formed, enhance the permeability of that layer.