The temperature and concentration variations in Pb-207 NMR shifts of Pb(NO3)(2) in aqueous solutions are analyzed in terms of exchange between aquated lead ion and the Pb(NO3)(+) ion complex according to the reaction PbNO3+(aq) = Pb2+(aq) + NO3-(aq). The analysis gives an enthalpy of dissociation of -3.0 +/- 0.2 kcal mol(-1) and an entropy of dissociation of -11.9 +/- 0.4 cal K-1 mol(-1).