ANX Sepharose 4 Fast Flow (low sub) and ANX Sepharose 4 Fast Flow (high sub) are two new media developed at Amersham Pharmacia Biotech. They are weak anion exchangers with different amounts of tertiary amine groups attached via a spacer arm to Sepharose 4 Fast Flow. They have been characterised by the separation of some model proteins under different conditions and by determination of breakthrough capacities for proteins of different molecular masses. Functional performance after storage in different solutions at ambient temperature has been monitored. Carbon release after storage at different pH and temperatures has been measured using the total organic carbon technique. The selectivity results show that these new media are interesting complements to already existing Fast Flow anion exchangers. They are very stable and can be especially useful in applications involving the purification of high-molecular-mass proteins.