AbstractPolar cell growth is regulated by auxin (Klämbt et al., 1992). It is essentially dependent upon exocytosis. Is exocytosis directly regulated by auxin?Aleurone cells secrete amylases, as well as other hydrolases, by exocytosis. In preliminary experiments, with 22 h of incubation, increasing concentration of N‐1‐naphthylphthalamic acid (NPA) parallels the inhibition of amylase secretion.A model system for secretion was designed. Barley aleurone layers, previously incubated in 1 μM GA3for 16 h, then washed extensively in the presence of 10 μM NPA for 10 min, were incubated finally for 2 h in GA3, NPA and/or auxins. NPA inhibits amylase secretion. Auxins completely abolished secretion inhibition at the optimal concentration of 1 μM.Aleurone layers contain 1.5 to 3 μM endogenous indole‐3‐acetic acid (IAA) and have a high capacity to accumulate and retain IAA. A 7‐fold accumulation occurred within 3 h after application of 20 μM radiolabeled IAA. A loss of about 10% could be measured within the following 4 h period in fresh media, independent of the presence of NPA.The inhibition of amylase secretion by NPA is not due to an inhibition of protein biosynthesis which was tested by the use of [