The distribution data were numerically analyzed for the extraction of trace lead(II)from 1.0 mol dm-3 (Li,H)NO3 media with toluene solutions of acidic organophosphorus compounds (HR), including di(2-ethylhexyl)phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic acid mono-2-ethythexyl ester (HEHEHP). The complex formulations were determined to be PbR2(HR), PbR2(HR)4, and Pb(NO3)R for the D2EHPA system and to be PbR2(HR)3, PbR2(HR)4, and Pb(NO3)R(HR) for the HEHEHP system. In this work, the equilibrium constants for the formation of these complexes were also given at 298 K.