Abscisic acid (ABA) caused an increase in free amino acid content of the fronds of L. minor, L. paucicostata and L. polyrrhiza within 6-12 h. This increase was followed by a temporary decline and a further, slower rise. Within 3 h of transfer to ABA, a substantial increase in medium amino N was detected indicating an increased rate of efflus and possibly implying effects on membrane permeability.