The electrochemical reduction of tributyltin (Bu3Sn+) at mercury electrodes has been investigated in aqueous media with nitrate and chloride electrolytes using the techniques of cyclic voltammetry, differential pulse polarography, and differential pulse voltammetry. In contrast to previous studies in mixed aqueous-organic media, the electrochemical processes were found to be surface confined. At low concentrations, corresponding to less than monolayer coverage of the mercury electrode, the initial charge transfer process occurs after adsorption at approximately -0.8 V vs. the saturated calomel electrode (SCE) and is essentially reversible, the complete process being described by the reaction Bu3Sn(bulk) +→Bu3Sn(ads)+ + e- ⇌ Bu3Sn(ads).. At more negative potentials (approximately - 1.3 V vs. SCE) a reversible tensammetric process is observed: Bu3Sn(ads) .⇌u3Sn(desorb). In concentrated chloride media this tensammetric process has a well-defined counterpart: Bu3Sn(ads)+⇌ Bu3 Sn(desorb)+ at approximately - 0.06 V vs. SCE, showing that strong adsorption takes place over almost the entire potential range available at mercury electrodes. At higher concentrations, corresponding to more than monolayer coverage of the mercury electrode, the electrochemistry is more complex and additional processes are observed.