The performance of a commercial hollow fibre ultrafiltration module processing skimmilk has been studied. The flux displayed a typical asymptotic behaviour with increasing transmembrane pressure, indicative of concentration; temperature had a small positive effect. The Leveque and the Grober laminar flow models underpredicted the experimental flux. The model was modified to include a concentration-dependent diffusivity term and to account for non-Newtonian rheological behaviour at high concentrations. The correlation which best fitted the data was Sh=0.087(Re)0.64(Sc)0.33