Electrochemical determination of metallothioneins (MTs) is widely used for environmental studies. In this paper, a new procedure for the quantification of MT by square wave cathodic stripping voltammetry has been developed and optimized. The determination is based on the complexation of cisplatin and MT and the subsequent reduction of the complexes at the electrode. In order to achieve highest sensitivity and resolution of the peak, an optimization of the experimental parameters has been carried out using experimental design methodology (response surface). Seven chemical and physical parameters namely pH, cisplatin concentration, buffer concentration, deposition potential, square wave frequency, amplitude of the pulse and step potential have been optimized. Method characterization has been performed, leading to a detection limit of 6 x 10(-12) Mol l(-1). This sensitivity is comparable to that of immunoassay, inducing that this procedure may also be used for MT quantification in tissue or serum. (C) 2003 Elsevier Ltd. All rights reserved.