Extraction of microamounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H ⁺B ^-) in the presence of N,N′-dimethyl-N,N′-diphenyl-2,6-dipicolinamide (MePhDPA, L) has been investigated. The equilibrium data have been explained assuming that the species HL ⁺, HL2, ML ² ₂ ⁺ and ML ²⁺(M ²⁺ = Ca ²⁺, Sr ²⁺) are extracted into the organic phase. The values of extraction and stability constants of the cationic complex species in nitrobenzene saturated with water have been determined.