MESSENGER^® (EDEN Bioscience Corporation) is a commercial product that contains Harpin Ea and has been shown to induce natural defense mechanisms in plants similar to those that would normally occur when a plant is attacked by diseases or insects. MESSENGER^® has been shown to stimulate growth of cotton (Gossypium hirsutum L.) and, in some cases, increase yield. A trial was conducted in Northwest Louisiana to determine cotton response to MESSENGER^® applied at 2.25 oz per acre at different cotton growth stages ranging from the 2-leaf stage to 3 weeks after first bloom. Although MESSENGER^® has been reported to significantly increase cotton yields in recent studies, none of the application timing combinations in this study resulted in seed cotton or lint yields that were significantly different from the untreated control. MESSENGER^® also had no significant effect on the total number of open bolls in 10 feet of row. MESSENGER^® has also been reported to reduce the number of hard- lock bolls and, although significant differences were found among the different timing regimes in this study, none resulted in significantly lower number of hard lock bolls compared with the untreated control.