The rate constants for the formation and dissociation of the 1:1 complexes of nickel with malonate and succinate ligands have been determined by a pressure-jump technique. The rates were determined at different temperatures and the activation parameters were calculated. The results indicate that, within experimental error, there is no change in the activation parameters for the formation reactions resulting from a change in properties of the ligand. This is consistent with a model in which the rate-determining step is the elimination of a water molecule from the inner hydration shell of the metal ion. The nature of the ligand only influences the rate of dissociation, as is shown by the activation parameters for this reaction.