A procedure for the determination of selenium species in seawater is proposed. The speciation scheme is based on different sample treatments followed by the quantification of Se(IV) by differential pulse cathodic stripping voltammetry. To remove the organic matter present in seawater which interferes in the electrochemical step a XAD-2 resin is used. So the selenite concentration can be directly determined. After passage through an IRA 400, selenide is collected in the percolated solution. Following conversion into the tetravalent state, selenium is determined. UV photolysis at basic pH is used to convert all the selenium species to Se(IV) which is the electroactive species. The procedure is applied to seawater samples.