The availability and utilization of nitrate by salt-marsh plants has been studied. All the species examined are able to assimilate nitrate, which appears to be the most important form of nitrogen available on the marsh. Species, from the strand line and lower marsh have higher nitrogen contents and nitrate reductase levels, than those from the upper marsh. Competition between species for nitrate is more important in the upper than lower marsh, because of low nitrate supply. Species such as Armeria maritima, Glaux maritima, Limonium vulgare and Triglochin maritima are able to compete more effectively for nitrate in the upper marsh than Puccinellia maritima, Salicornia europaea, Suaeda maritima, Spergularia media and Spartina×anglica. The results indicate there is an increase in nitrogen supply down the marsh, which may be associated with the input of nitrate during tidal innundation.