Various aspects of salt excretion from leaves o( Aeluropus were investigated. Salt excretion exhibited an optimum-type of curve when measured against external salt concentration, while sodium content of the leaves increased linearly. The 'relative excretion', i.e. rate of excreted ions : change in leaf ion content, was maximal in the low salt concentration range, and decreased when external sodium chloride concentration increased. Concentration of the excreted droplets was higher than the external coneentration when the leaves were exposed to low salt concentrations in the medium, but the reverse occurred when the external salt concentrations were high. The excretion process was sensitive to water-stress conditions, caused either by high external salt concentrations or by exposure to dry atmosphere. A considerable fraction of the leaf sodium content in sail-treated leaves was only slightly available for excretion. Salt excretion in Aeluropus was enhanced by light. Such enhancement was indirect and is attributed to the increase of salt transport via transpiration stream.Selectivity of the salt-excretion mechanism is in favour of sodium and against potassium. On the other hand, potassium has a high affinity for the accumulation systems within the leaves. The ecological significance of the results is discussed.