The kinetics of aluminum and beryllium extraction by mono(2-ethylhexyl)phosphoric acid (M2EHPA) is studied using a stirred transfer cell. M2EHPA has high surface activity and forms reverse micelles in the organic phase. The formation of a 1:1 complex of the metal ion and the dissociated M2EHPA anion in the aqueous phase is found to he rate-determining. The formation of reverse micelles does not affect the extraction rate, and rapid attainment of the extraction equilibria observed otherwise in the shaking experiments is considered to he caused by the large interfacial area due to the lowering of interfacial tension.