Polarographic investigation of a series of potassium O-alkylxanthates in acetone has shown that they undergo the following processes at a mercury electrode. 2Hg0+6ROCS22Hg(S2COR)3-+4e. 2HgII(S2COR)3-+Hg02HgII(S2COR)2+2e (where R is an alkyl group). Analysis of the two waves corresponding to these processes shows qualitative agreement with theoretical predictions for such a mechanism, although the system is complicated by adsorption phenomena. The complex HgII(S2COC4H9)2 has actually been isolated, and strong evidence for the existence of HgII(S2COR)3- complexes has been obtained. Behaviour in other media is briefly reported.