The kinetics of the Ti(IV)/Ti(III) couple in 0.4-9 M H2SO4 were investigated at the mercury drop electrode using dc polarography and square wave voltammetry with forward and reverse scans. The experimental results obtained at low and at high H2SO4 concentrations were modelled and interpreted quantitatively on the basis of a CE-ECE reaction scheme. Indications on the nature of the electroactive forms of Ti(IV) in H2SO4 are also given. (C) 2004 Elsevier B.V. All rights reserved.