Americium (Am) and europium (Eu) extraction from HN0₃ and HC10₃ media by a synergistic mixture of 2,6-bis(l-aryl-lH-tetrazol-5- yl)pyridines (ATP) with chlorinated cobalt dicarbollide (CCD) was studied by using m-nitrobenzotrifluoride, phenyltrifluoromefhyl sulfone, and 1,2-dichloroethane as diluents. We examined the effects of diluents, of the aqueous phase composition and the nature of substituents in the ATP aryl ring on Am/Eu extraction efficiency and selectivity. The Am/Eu separation factor was found to be close to 100 at the optimal ratio of ATPs:CCD∼ 1:1. We also studied the extraction of ⁸⁵Sr, ¹³⁷Cs and ¹³³Ba; a PhATP-CCD mixture provided the separation of the Sr/Ba pair with a factor of 35. A high resistance of 2,6-bis-aryltetrazolyl pyridines to 6 M nitric and perchloric acids at 95 °C was demonstrated.