In both TAMCOT CAMD-E and Stoneville 213, MC treatment significantly reduced vegetative dry weight, but differences in boll dry weight, total plant dry weight, and number of bolls were not affected significantly. Early, recommended, and late MC treatments increased seedcotton yield of Stoneville 213, but not of TAMCOT CAMD-E. Correspondingly, lint yields were increased in Stoneville 213 but decreased in TAMCOT CAMD-E. Early MC treatment increased fiber length and length uniformity in Stoneville 213 but not in TAMCOT CAMD-E. Yield increases in Stoneville were associated with increased boll size, improved light penetration into leaf canopy, improved relative fruitfulness, higher harvest index, and increased production rate index.