This article presents a study of dietary supplements available on the Polish market. The supplements
comprised a large group of products with selenium content declared by the producer. The study involved
determination of dissolution time under different conditions and solubility as well as content and speciation
of selenium. The total content was determined as well as organic selenium and the inorganic forms
Se(IV) and Se(VI). The organic selenium content was calculated as the difference between total Se and
inorganic Se. The values obtained were compared with producers’ declarations. The work is the first such
study of selenium supplements available on the market of an EU Member State.