Cotton strength provided by high volume instruments (HVI) is directly affected by changes in fiber moisture and indirectly by the amount of crimp remaining after fiber preparation. Additionally, moisture and crimp are also affected by humidity in the air when fiber are prepared for strength testing. Experiments were conducted to measure strength changes caused by moisture in samples delivered for testing. Other experiments were conducted to measure changes caused by environmental humidity. The strength-moisture effect, based on 50 cottons at six moisture levels was 1.5 and 1.7 gf/tex/% for two different HVI systems. The strength-humidity effect, was based on testing 50 cottons and six HVI calibration cottons with one instrument system (i. e., 0.27 gf/tex/%RH).