ABSTRACT The extraction of the alkali ions by the 25,27-Dicarboxy-26,28-dimethoxy-5,ll,17,23-tetra-tcrt-butylcalix[4]arene (LH2) in 1,2-dichloroethane has been studied. The existence in the organic phase of the extracting species LHM (M = Na, K, Rb, Cs) is shown by conventional liquid-liquid extraction procedures and confirmed by mass spectrometry. The observed selectivity (Na > K > Rb > Cs) suggests that the dicarboxycalix[4]arene group plays a role similar to that played by the crown-ether containing four or five oxygens in ionizable crown-ethers. It is shown that the extraction of lithium takes place via the formation of the LLi2 species.