The availability of high-speed tensile testing machines has made it possible to predict yarn performance more accurately. However, results obtained from new, high speed testing machines do not show the same results as those from older, slow speed testing machines. The testing machines used were USTER^®Tensojet, USTER^®Tensorapid, and Constant Tension Transport by Lawson-Hemphill. The data presented is from 21different yarns which were spun on three different spinning systems from 7 different cotton/polyester blends, together with 29 other cotton and cotton/polyester yarns. The method of yarn analysis was developed by evaluating the yarn data. Single-strand breaking tenacity and breaking elongation was measured for each yarn. Testing speed was considered as a possible factor influencing the tenacity-elongation characteristics in a yarn. The experimental results obtained show that the tenacity value obtained from the various test increases linearly with the logarithm of the testing speed.