Selenium is an essential trace element in mammals, as a result of the requirement for the encoded amino acid seleno-l-cysteine (Sec) that is present in a range of selenoproteins. Selenium is also present in other forms in biological systems, including selenomethionine and inorganic species. While the role of some Sec-containing proteins has yet to be fully resolved, some of these, in particular isoforms of the thioredoxin reductase, glutathione peroxidase and methionine sulfoxide reductases, play key roles in modulating oxidative stress. Consequently, there is considerable interest in the reactions of selenium species with oxidants, the reasons for the biological use of selenium versus sulfur and the potential use of low-molecular-mass selenium species as protective agents against oxidative damage. Here we review the kinetics and mechanisms of the reactions of oxidants produced during inflammation, with low-molecular-mass organoselenium compounds (e.g. selenoethers, diselenides and selenols). While selenium has some similar properties to sulfur, it typically exhibits greater reactivity with oxidants (e.g. hydrogen peroxide, radicals, singlet oxygen and hypochlorous, hypobromous, hypothiocyanous and peroxynitrous acids), and there are considerable differences in the subsequent reactivity and ease of repair of the resulting oxidation products. These data provide important insights for the development of therapeutic compounds.