Indole-3-acetic acid (5-10 μM) was found to induce an increase in the potassium, sodium, and calcium permeability of the plasmalemmal vesicles isolated from maize (Zea mays L.) coleoptiles. Based on the results obtained, a mechanism of IAA action at the membrane level was offered. According to this mechanism, IAA stimulates proton secretion by the plasmalemma H⁺-ATPase via sequential activation of the plasmalemma-bound anion, calcium, and Ca²⁺-dependent K⁺ channels. The earliest effects of IAA are apparently related to the activation of the anion and Ca²⁺ channels.