Hollow fibre membrane ultrafiltration is an important industrial process. The process is, as expected, limited by concentration polarisation and fouling. Introduction of long gas slugs into the ultratiltration feed stream enhances filtration flux. However, a need still exists for quantification of the enhanced process in order to predict flux for design and optimisation purposes. This work shows how analogous, one-dimensional (1D) mass and momentum boundary layer analyses can predict filtration flux. An improved 1D boundary layer analysis is obtained for developing laminar flow in pipes in order to effect the required flux predictions. The flux prediction model is validated with experimental data and the model gives good insight into the enhancement mechanisms and their relative importance in the observed mass transfer enhancement. (C) 2004 Elsevier Ltd. All rights reserved.