The extraction of Am, Cm, Eu, and Ce(III) tracers from nitric acid in the presence of Al(NO3)(3) by 18-crown-6 (18C6) or mixtures of 18C6 and chlorinated cobalt dicarbollide (ChCoD) in nitrobenzene solutions was investigated. The partitioning of 18C6 between nitrobenzene and the aqueous phase was also investigated. In the presence of Al(NO3)(3), 18C6 is selective for Ce over Am, Cm, and Eu. The extraction of these same metals by ChCoD is suppressed by Al(NO3)(3) The extraction of these metals is a complicated function of the 18C6-ChCoD concentration ratio. The probable formation of a 1:1 18C6:ChCoD complex and the effects of ionic strength and pH on the extraction are discussed.