Indole-3-Acetic Acid (IAA) is a phytohormone, found to be abundant during the early stages of fiber development in cotton (Gossypium hirsutum L). When applied exogenously, it has been shown to increase fiber initiation; however, other effects are unknown. Therefore, genotypes differing in fiber length potential were placed in a field study to observe the effect of exogenous IAA on yield components and fiber properties. Field studies were conducted from 2008 to 2010 in College Station, TX. One boll per plant was treated with IAA at 4, 12, and 20 days post anthesis (dpa) to coincide with different phases of fiber development. Results showed a significant year interaction with IAA treatment and genotype. In 2009, the plants responded to IAA application. Bolls treated with IAA had increased lint percent due to increased fibers per seed. Genotypes with inherently longer fiber length were negatively affected by treatment with IAA, suggesting that a higher number of fibers per seed may decrease fiber length through competition. There was a genotype by IAA treatment interaction for lint percent, fibers per seed, fiber length, fiber elongation and seed index. However in 2008 and 2010 results were not consistent with 2009; possibly due to differences in environmental conditions. This research does indicate that genotypes differ in IAA sensitivity and suggests that previous work on IAA should be classified as genotype specific. Future work should include determining the amount of IAA that permeates and interacts with ovules to determine the most effective rate, form and application timing on yield components and fiber properties.