Pertraction or extraction by liquid membranes is a new, prospective separation method for recovery and concentration of antibiotics from their dilute aqueous solutions. Mixture separation by pertraction is a combination of two, widely used and consecutively applied operations: extraction of solute from the feed solution and stripping of the enriched organic phase by another solution. In pertraction processes solute extraction from the feed and its stripping from the extract are combined in a way to provide a maximum yield with minimum extractant losses and energy consumption.The purpose of the present work was the study of continuous tylosin removal from its aqueous solutions in a multistage rotating disc pertractor, applying a counter-current flow. n-Decanol and n-octanol were used as membrane liquids. The effect of the feed solution residence time on pertraction efficiency was studied. A mathematical model describing the process was used for the evaluation of the stage efficiency. (C) 2003 Elsevier Science B.V. All rights reserved.