Previous studies with ytterbium in oxalate solutions have demonstrated that the determination of concentrations by radioassay would permit the evaluation of equilibrium constants for the system. The present paper describes results of similar experiments with neodymium and cerium. Since the lighter rare earths have greater ionic radii, it was expected that the degree of complexing would be less and a lower solubility in oxalate would result. The data presented in this paper for neodymium and cerium confirmed the lower solubility but indicated that the complexes were not substantially weaker. The behavior of cerium was markedly different from that of ytterbium and neodymium in that definite evidence was found for the formation of a trioxalate complex.