This paper deals with the purification of a semi-solid liposome (SSL) preparation which consists in the removal of free hydrogel present in external solution. Two separation methods, a cross-flow ultrafiltration and a centrifugation have been investigated and compared. Experiments were carried out in static and in vibrating membrane systems and in a batch and semi-batch centrifuges. As filter systems, membrane processes using different membranes consist in a diafiltration step until the free hydrogel were almost completely eliminated followed by a concentration step. Different membranes were tested. Due to a low selectivity, permeate flux and hydrogel removal rate were small obtained with a static membrane filter. However, a vibrating filter system and a centrifuge were both suitable; hydrogel removal was close to the required value. only a few amount of SSL was lost entrapped in the membrane or degraded by the circulation. In the view to develop an industrial plant, a membrane filter system was preferred to a centrifuge because of its flexibility, compactness and cost. (C) 2004 Elsevier B.V. All rights reserved.