The mass transfer in a parallel-plate concurrent dialysis system coupled with ultrafiltration operation is investigated theoretically and experimentally in this study. The separation efficiency improvement in mass transfer and flow stream composition variation along the parallel-plate channel were investigated analytically using the Frobenius series method. The mass transfer efficiency enhancement results by introducing a transmembrane pressure in the device are represented graphically and compared with those in a conventional dialysis device considering only the concentration difference as the driving force. The analytical results show that a dialysis system coupled with ultratiltration can effectively enhance the separation efficiency compared with operation without transmembrane pressure. Moreover, the theoretical predictions are in qualitative agreement with the experimental results. (c) 2006 Elsevier B.V. All rights reserved.