Cotton strength measurements were made at constant rates of extension to determine the effect of speed on the measurement of 1/8 gage elongation. Six extension speeds from 0.4 to 50.0 cm/min were investigated. Elongation was measured on fifty-four experimental cottons including eighteen varieties from thirteen states. Measurements at a speed comparable to Stelometer testing gave elongation values 26% higher than expected by the Stelometer methods. When the rate was increased to a speed comparable to High Volume Instrument testing, the average elongation dropped by 15%. There were considerable differences between individual cottons in the amount of elongation loss at the higher speed. Neither cotton variety nor growth area appeared to be the determining factor causing elongation changes.