AbstractResearch suggests strong inter-relationships between physical exercise, levels of brain-derived neurotrophic factor (BDNF), levels of estrogen, and the menstrual cycle, and yet no single study has examined these factors collectively in humans. The current study assessed the effect of an acute bout of vigorous aerobic exercise (20 minutes of stationary cycling at 80% of heart rate reserve) on serum BDNF and estradiol in healthy, eumenorrheic women, ages 18-28. In addition, this study determined whether basal BDNF or the exercise-induced increase in BDNF varies throughout the menstrual cycle. Thirty-four subjects were assigned to an experimental (n = 27) or control condition (n = 7). Exercise transiently increased both estradiol (51.2%) and BDNF (23.6%), and basal levels of BDNF and estradiol predicted the magnitude of the exercise-induced increases. Basal BDNF did not vary significantly throughout the menstrual cycle. Exercise-induced changes in BDNF did not correlate with menstrual cycle day or basal estradiol. Basal estradiol and basal BDNF showed a marginally significant positive correlation. Taken together, these results indicate that brief, vigorous aerobic exercise is sufficient to elevate both BDNF and estradiol in healthy women and that the menstrual cycle dramatically influences the magnitude of exercise-induced changes in estradiol, but not BDNF