With hypocotyls of Helianthus annuus, coleoptiles of Zea mays and radicles of Vicia faba seedlings the relations between auxin distribution and the development of electric potential differences were examined. A. Experiments with Helianthus seedlings. 1. Removal of one of the cotyledons produces a transversal potential difference in the hypocotyl between the intact flank and that without cotyledon. With 10(-3)m KCl as contact solution the positive pole always lies on the intact side. 2. Unilateral supply of synthetic auxins in aqueous solution calls forth a comparable potential difference. The electric effect of the growth substances examined corresponds to their growth promoting power: G.A.<2,4-D