Sodium chloride (NaCl) concentratíons 200 to 900 mM enhanced the photosynthetic rate (Pn) both in whole leaves and in mechanically isolated, intact mesophyll cells of a salt marsh halophyte Sesuvium portulacastrum wilh a maximum at 600 mM NaCl. These changes were in agreement with changes in chlorophyll concentration in leaves. Though the increasing salt concentratíons resulted in leaf succulence, no change in the photosynthetic carbon pathway was observed.