7-Methoxy-1-naphthaleneacetic acid is an inhibitor of auxin action in plants. 7-Methoxy-1-naphthaleneacetic acid inhibits polar auxin transport and tropic responses associated with asymmetric auxin distribution in Arabidopsis and maize. 7-Methoxy-1-naphthaleneacetic acid inhibits auxin transport mediated by AUX1, PIN, and ABCB proteins expressed in yeast.