The comparative electrochemical behaviour, in aqueous solutions, of the Dawson lacunary anion [P2W17O61](10-) and of the Fe-III Cu-II, Co-II, Ni-II, Mn-III and Mn-II substituted Dawson lacunary heteropolyanions is presented. The literature concerning the latter heteropolyanions has been reviewed and completely new data are presented. The electrochemical behaviour observed for the reduction of the tungsten oxo centres, for all the heteropolyanions investigated, was found to be pH dependent. Electrochemical evidence for the presence of the Fe-III, Cu-II, Co-II and the Mn-II and Mn-III cations in the ejected tungsten position was obtained with the N-II cation possessing no electroactivity.