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A variety of complexes of cadmium with mono-and di-carboxylic acids in aqueous solution were investigated using l 1 3Cd NMR spectroscopy. A single averaged chemical shift was obtained even at reduced temperature, showing that the cadmium-monocarboxylate complexes are undergoing rapid exchange in solution. Using the known stability constants, the individual chemical shifts were calculated to be in the range F -22 to -24 and -39 to -40 for [CdL] + and [CdL,] (L = carboxylate) species respectively: carboxylates with higher basicity tend to increase the shielding of the cadmium in the complexes. In case of dicarboxylic acids HO,C(CH,),,CO,H(n = 0-3) the ' 13Cd nucleus showed greater shielding with increasing n. The upfield chemical shift observed for the dialkyl-substituted malonate complexes of Cd" compared to the malonate complex is caused by the steric effect hindering ring formation.Cadmium-1 13 NMR spectroscopy has been widely used as a probe of the metal-ion binding sites in many biological systems, such as metallothionein 1 * 2 and metal lo enzyme^,^-^ as ' 13Cd