A detailed, qualitative, investigation of the behaviour of lead complexes with fulvic substances has been carried out using several polarographic techniques, e.g d.c. polarography, a.c. polarography, normal and differential pulse polarography and cyclic voltammetry. The mercury drop electrode was used for this study. It is shown that under the conditions used (pH∼6) the charge transfer process is reversible, the complexes are labile and the adsorption of fulvic acids and fulvic complexes occurs on the electrode. The implications of these results, with regard to the use of the various amperometric titrations for the measurement of the complexing capacity of natural waters, are discussed.