The electrochemical reduction of 5-mercuriuridine monophosphate, diphosphate, and triphosphate nucleotides at mercury electrodes in aqueous solution is reported. Both diffusion-controlled and surface-confined electrode reactions were observed. In aqueous KCI electrolytes, the diffusion-controlled pathway involved the two-electron reduction of the carbon-mercury bond to give the parent nucleotide. In D2O solution, the corresponding 5-deutero nucleotide was formed. All three mercurated nucleotides formed compact monolayers on the mercury electrode surface in accord with the Langmuir isotherm. Anomalies in the voltammetric behavior and the adsorption isotherm of the 5-mercuriuridine monophosphate in KCI solution are ascribed to the formation of polymeric anions by coordination of the mercury substituent with the nitrogen of the pyrimidine ring. The reduction mechanism of the surface-confined nucleotides is more complex than the diffusion-controlled reaction. For the surface reaction, two one-electron steps (an EE reaction) were observed, The organomercury radical (RHg.) one-electron intermediate formed a compact surface layer that was stable on the voltammetric time frame. This species participates in a surface square scheme that is operative at mercury electrodes over the pH = 2-12 range. Finally, evidence is presented that implicates kinetically controlled nucleation phenomena in the surface reactions of the adsorbed intermediates in the electrode processes.