The gas-exchange method has been used to measure net carbon dioxide assimilation at different temperatures and irradiances in leaves of salt-treated and untreated plants of Spartina anglica. The results together with those of the CO2 compensation point and leaf anatomical data clearly indicate that Spartina anglica is a high photosynthetic capacity plant. At high temperatures and irradiances leaves of the salt-treated plants were able to maintain net photosynthesis, in contrast to the behaviour of leaves of untreated plants. The ecological significance of these results is discussed