The anodic oxidation of ethyl xanthate (EX-) on a lead surface is characterised by a voltammetric prewave that occurs at underpotentials to lead ethyl xanthate formation. The prewave arises from the chemisorption of ethyl xanthate. The potential dependence of ethyl xanthate coverage fits the Frumkin adsorption isotherm, [theta/(1 - theta)]exp(2 theta) = 8.98 X 10(14)[EX-]exp(1.1FE/RT).