The stoichiometry of the reaction between lead dioxide suspension and EDTA was studied by derivative polarographic titration and determination of the products. Four moles of Pb(IV) are reduced per mole of EDTA with moderate speed at room temperature in sulphuric acid solutions. Four moles of carbon dioxide and 3 moles of formaldehyde are the products of the oxidation of 1 mole of EDTA. One mole of N-hydroxymethylethylenediamine is also thought to be produced. The overall reaction may be written as 4Pb(IV) + EDTA + 4H(2)O-->4Pb(II) + 4CO(2) + 3HCHO + H(2)NCH(2)CH(2)NHCH(2)OH + 8H(+). Ethylenediamine is also partly produced if a large excess of lead dioxide is used.