FINISH is a new cotton defoliant which contains two active ingredients: ethephon and cyclanilide. Cyclanilide is an ethephon synergist which enhances defoliation and inhibits regrowth even at low temperatures. The overall purpose of this research was to demonstrate the efficacy of FINISH in comparison to other defoliants, and to determine the mechanism by which cyclanilide enhances ethephon efficacy. When cyclanilide was combined with ethephon (Prep) approximately 90% defoliation was detected in cotton compared to 70% defoliation when Prep was applied alone. Prep induced 90% boll opening when applied alone or in combination with cyclanilide suggesting that cyclanilide does not interfere with Prep efficacy in boll opening. Regrowth was less when cyclanilide was combined with Prep. In the Midsouth and Southeast regions, FINISH enhanced both defoliation and boll opening. Some combinations of Prep with other defoliants such as Folex and Dropp resulted in adequate defoliation or boll opening; however, FINISH has the advantage of being a single package harvest aid. Combining NPA, a known auxin transport inhibitor, with low rates of ethephon resulted in enhanced defoliation similar to cyclanilide combined with ethephon suggesting that cyclanilide may act as an auxin transport inhibitor thereby enhancing ethephon efficacy. This hypothesis was further supported by experiments that demonstrated that cyclanilide can inhibit radiolabled auxin movement through corn coleoptiles similary to TIBA, another known auxin transport inhibitor. Furthermore, binding studies demonstrated that cyclanilide competes with ³H-IAA binding in plasma membranes. Although cyclanilide binds with less affinity than IAA, our results suggest that cyclanilide could be inhibiting auxin transport by interacting with an auxin efflux protein.