The extraction of Pb(II) from 1.0 M KCI media by the commercial extractant Cyanex 302 dissolved in toluene has been studied as a function of the total extractant concentration, the equilibrium pH and the total metal concentration. The influence of bis(2,4,4)-trimethylpentyi)dithiophosphinic acid, one of the minor impurities of Cyanex 302 and also the major component in Cyanex 301, on the extraction of lead has also been examined by studying the extraction of the metal ion by Cyanex 301. Experimental data have been treated numerically by means of the computer program LETAGROP-DISTR, and can be explained by assuming the extraction of the species PbR2(HR), PbL2(HL) and a mixed complex of stoichiometry PbLR(HR), HL being bis(2,4,4-trimethylpentyl)-dithiophosphinic acid, the active component of Cyanex 301 and HR standing for bis(2,4,4-trimethylpentyl)monothiophosphinic acid, the active component of Cyanex 302. The stoichiometric equilibrium constants of the extraction processes are also given.