Contralateral acoustic reflex thresholds (ARTs) were determined daily in 10 normal women and 10 men, aged 18-24, in response to a broad-band noise, over a 32-day period. Mean ARTs for men vs women over the period differed by only 1.55 db, but for women a stimulus level of about 6 db more was required to elicit ART over Days 1-6 of the menstrual cycle than over Days 7-26 (p less than .01). There was furthermore an increase in sensitivity in the luteal phase (Days 15-19) of the cycle. It appears that the changes in ART throughout the cycle mirror, and may reflect, concomitant changes in the hormonal (estrogen and progesterone) levels. Changes in ART over the cycle may thus be explained by hypothesizing that the ART is an aspect of sensorineural behavior affected by hormonal concentrations to which a number of other auditory phenomena are known or thought to be related.