Fiber quality is the result of interactions between genetics and environment. Fiber property variability has been related to boll location. Fiber properties may be modified by soil water availability and growth regulating chemicals. Cotton (Gossypium hirsutum L.) was grown in Corpus Christi, Texas under rainfed and irrigated conditions and treated with mepiquate chloride (MC). Fiber lengths were highest in earlier set first position rainfed bolls, while fiber maturity values were higher in later set first position bolls (rainfed and irrigated). Comparisons of fiber from untreated and MC treated plants revealed a few significant differences in 1994 and none in 1995. The differences were pronounced in 1996 which was characterized by very low rainfall. Mepiquat chloride treated plants had first position bolls with longer fibers and higher maturity values than untreated cotton. The effects of MC on cotton fiber properties were not limited to early set first position bolls.