In this paper, optimal operating policies for HPLC separation processes based on a closed-loop recycling strategy are presented. Successful application of closed-loop recycling HPLC processes had been reported, mainly in the pharmaceutical industry, but there is still limited knowledge about the dynamic behaviour of this process and little work on optimal operation of closed-loop recycling systems has been presented in the open literature. This paper investigates different operating policies for a closed-loop recycling HPLC system using an equilibrium-dispersive model coupled with a dynamic optimisation technique. The operating policies include: conventional recycling, recycling with peak shaving and recycling with peak shaving and multiple feed injection. The determination of optimal operating policies is aimed to maximise the amount of purified product(s) and thereby achieve better column performance whilst keeping the matrix cost constant. The practical implementation of these operating policies will also be considered. (C) 2003 Elsevier Ltd. All rights reserved.