The transport of chromium(VI) through a flat-sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921-based flat-sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. (C) 2003 Society of Chemical Industry.