Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B^-) in the presence of N, N, Ń, Ń - tetraisobutyl - 2, 6 - dipicolinamide [T(iBu)DPA, L] has been investigated. The equilibrium data have been explained assuming that the cations HL⁺, HL⁺ ₂, ML ³ ₂ ⁺ and ML³ ₃ ⁺ (M³⁺ = Eu³⁺, Am³⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.