MANY Procellariiform seabirds make their living flying over vast expanses of seemingly featureless ocean waters in search of food, The secret of their success is a mystery, but an ability to hunt by smell has long been suspected(1-7). Here we present experimental evidence that Procellariiform seabirds can use a naturally occurring scented compound, dimethyl sulphide, as an orientation cue, Dimethyl sulphide has been studied intensely for its role in regulating global climate(8-11) and is produced by phytoplankton in response to zooplankton grazing(12). Zooplankton, including Antarctic krill (Euphausia superba)(13), are in turn eaten by seabirds and other animals(14). Results from controlled behavioural experiments performed at sea show that many Procellariiforms can detect dimethyl sulphide, and that some species (for example, storm petrels) are highly attracted to it. To our knowledge, this constitutes the first evidence that dimethyl sulphide is part of the natural olfactory landscape overlying the southern oceans.