Properties of pseudopolarograms of inert complexes of metal ions and polydentate ligands are described and their application in speciation measurements is discussed. Pseudopolarography can be used to distinguish labile metal complexes from the inert complex species and to estimate the distribution of metal ions at a trace level. Pseudopolarograms of Pb(II)-nitrilotriacetic acid chelate were analysed and the stability constant log(k) = 11.9 of the complex, the pseudopolarographic half-wave potential E(1/2) = - 0.64 V vs Ag/AgCl, the charge transfer coefficient alpha = 0.4 and the standard rate constant k(s) = 2 x 10(-3) cm/s(-1) of its redox reaction were determined.