The effects of high night temperatures on the physiology and biochemistry of cotton’s first day flowers and their subtending leaves during reproductive development were evaluated in growth chamber experiments conducted at Altheimer Laboratory of the University of Arkansas. Plants were exposed to higher than optimum temperatures (30ºC compared to 24ºC) from 20:00- 06:00 for a total period of two weeks after plants had reached squaring (approximately 4 weeks after planting) and flowering stage (approximately 8 weeks after planting). Main-stem leaves were collected at 6:00 at the end of each week and analyzed for their carbohydrate and antioxidant content. The results are still being analyzed.