The interaction between lead(II) and methanesulfonate ions was studied by conventional d.c. polarography at 2.0 M ionic strength and pH 4.0. Two stepwise lead complexes are formed in solution : [Pb(CH3SO3)](+), beta(1) = 1.76 +/- 0.03 M(-1) and [Pb(CH3SO3)(2)], beta(2) = 0.25 +/- 0.05 M(-2) which are reversibly reduced at the DME. At high ligand concentrations, above 1.0 M, a third lead complex, [Pb(CH3SO3)(3)](-), beta(3) = 0.30 +/- 0.07 M(-3), is formed.