The conformational effects upon complexation of calcium (II) and lanthanide (III) ions by 2,3-dicarboxy-[beta]-cyclodextrin (DC-[beta]CD) have been studied by 1H-, 13C-, and 17O-n.m.r. spectroscopy. The complexation of Ca2+ by DC-[beta]CD involves conformational transitions at metal/ligand ratios ([rhov]) of 0.25 and 0.5 with predominant changes in the resonances of C-1,4,5. For the La3-DC-[beta]CD complex (up to [rhov] 0.3), a structure involving two La3+ per DC-[beta]CD macrocycle, each coordinated to 8 oxygen atoms, is proposed. Optical rotation data indicated similar conformational behaviour on complexation of Ca2+ with DC-[beta]CD and dicarboxyamylose (DCA), whereas dicarboxycellulose (DCC) showed a substantially larger change in conformation. Static and dynamic light scattering indicated aggregation of DCA and DCC on complexation with Ca2+, with a concomitant reduction of the hydrodynamic radius (Rh).