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+, HL+2, ML2+2 and ML2+3 (M2+ = Ca2+, Sr2+) 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.