A novel method using n-hexadecane/water two-phase flow to abate concentration polarization in ultrafiltration was proposed. Compared with a corresponding air-sparged ultrafiltration, the n-hexadecane/water ultrafiltration was shown to have a higher permeate flux when concentrating a crude lipase solution. This was attributable to the much higher shear force induced by n-hexadecane droplets, and the reduction in concentration polarization was thus more pronounced. The range of injection factor resulting in bubble flow was broader in the n-hexadecane/water ultrafiltration than in the air-sparged ultrafiltration. In addition to the permeate flux, the recovery of lipase activity was also enhanced, and enzyme inactivation due to the use of the two-phase flow was not concerned. The benefits from the n-hexadecane/water two-phase flow were found to be common in various ultrafiltration practices. (C) 2004 Elsevier B.V. All rights reserved.