A detailed investigation of the Pb(II)/OH- system has been made in NaClO4 media at 25 degreesC. Combined UV-vis spectrophotometric-potentiometric titrations at [Pb(II)](T) less than or equal to 10 muM using a long path length cell detected only four mononuclear hydroxide complexes. The values of log *beta (1q), for the equilibria Pb2+(aq) + qH(2)O <----> Pb(OH)(q)((2-q)+)(aq) + qH(+)(aq), were -7.2, -16.1, -26.5, and -38.0 for q = 1-4, respectively, at ionic strength I = 1 M (NaClO4). Similar results were obtained at I = 5 M (NaClO4). No evidence was found for higher order complexes (q > 4) even at very high [OH-]/[Pb(II)] ratios, nor for polynuclear species at [Pb(II)](T) less than or equal to 10 muM. Measurements using Pb-207-NMR and Raman spectroscopies and differential pulse polarography (DPP) provided only semiquantitative confirmation. The mononuclear Pb(OH)(q)((2-q)+)(aq) complexes are the only hydrolyzed species likely to be significant under typical environmental and biological conditions.