A new method for measuring the anion transport activity of Band 3 in the erythrocyte inside-out vesicles(IOVs)was presented.Impermeable IOVs containing 80mmol/L dipicolinic acid (DPA)were obtained by pressing the IOVs through a No.9 gauge needle in DPA- containing medium.Efflux of DPA from the IOVs into Tb³⁺-containing transport buffer was monitored fluorometrically. The technique is highly sensitive, reproducible and much convenient as well.