Data are presented from an experimental investigation of dynamically-formed membranes (DFMs) operated under conditions of low pressure. Hydrous zirconium oxide-polyacrylic acid (Zr-PAA) DFMs have been formed on a composite, ceramic/metal mesh microfiltration (MF) membrane at pressures and cross-flow velocities of 1.1 MPa and 2.67 m/s, respectively. Similar conditions were employed during operation. After correcting for the effects of concentration polarisation the salt concentration was shown to have a significant effect on the intrinsic rejection and permeability of the DFMs. Permeation trials against non-ionic solutes revealed that the decrease in permeability could be attributed to physical changes in the membrane material. Further processing of the corrected data showed the Brian correlation to give a reasonable representation of mass transfer under the turbulent flow conditions employed during the study.