The influence of some organic expanders on the formation of lead-sulphate has been studied by means of potentiostatic transients. The experimental data have been discussed according to the theories which have been proposed in the literature for the electro-crystallisation of lead-sulphate and lead. The discussion of the data obtained confirms the inhibiting effect of the expanders on lead sulphation. in fact, the tests showed that, when the expanders are added to the electrolyte, a longer time is required to reach the current maximum of the i(t) curve and a reduction of its intensity. According to the theoretical interpretation, this finding indicates a decreasing of the kinetic constant of the solid state process. The analysis of the i(t) transients obtained during the sulphate reduction revealed an influence of expanders only when the sulphate layers has been formed in their presence. Thus, it seems that the adsorption of the organic expanders on lead is of primary importance for their action while adsorption on lead-sulphate appears to be negligible. (C) 2000 Elsevier Science S.A. All rights reserved.