From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb2+(aq)+SrL22+(nb)⇆PbL22+(nb)+Sr2+(aq) taking place in the two-phase water-nitrobenzene system (L=15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated: logKex (Pb2+,SrL22+)=3.0. Further, the stability constant of the PbL22+ complex in nitrobenzene saturated with water was calculated: log βnb(PbL 22+ )=17.8