Boll openers are often used when terminating a crop in order to open immature bolls, hasten harvest, and possibly increase yield. Studies were conducted in 1996 and 1997 to determine the boll opening effectiveness of Prep (ethephon), Starfire (paraquat), CottonQuik (ethephon + aminomethanamide dihydrogen tetraoxosulfate), and Finish (ethephon + cyclanilide). Field locations in 1996 were at Rocky Mount and Lewiston, and at Rocky Mount and Clayton in 1997. Treatments were an untreated check, Prep 1.33 and 1.67 pt/a, Starfire 6, 11 , 16, and 24 oz/a, CottonQuik 2 and 3 qt/a, Finish 1.0 and 1.5 qt/a, and Def/Folex 0.5 pt/a. All treatments with a boll opening material also received 0.5 pt/a of Def, and an additional treatment of 1.5 qt/a of Finish alone was added in 1997. Plots were four rows wide and 50 feet long. Hand harvests were taken every 3-4 days from 3 meters of one inside row of each plot. Data were analyzed as percent of total harvestable yield on each harvest date in 1996 and percent open bolls in 1997. Additionally, plots were rated visually for defoliation effectiveness.