The effect of sex hormones on airway function has not been well studied in spite of much evidence to suggest that they are important. We asked if the normal physiologic variation in hormone levels during the menstrual cycle resulted in changes in airway responsiveness and pulmonary function that were not clinically apparent. Nine women with asthma and with normal menstrual cycles but not taking systemic asthma medication were asked to chart temperatures, asthma attacks, and use of asthma medication for four menstrual cycles. We measured baseline spirograms, skin and airway responsiveness to histamine, and serum levels for estradiol, progesterone, and testosterone on approximately day 7 and day 24 of two consecutive cycles. None of the women reported cyclic asthma symptoms, and review of subjects' charts demonstrated no menstrual variation in asthma attacks or use of asthma medications. We found no differences in forced vital capacity or FEV1 early compared to late in the menstrual cycle. Neither did we find a change in airway responsiveness, as indicated by the histamine dose causing a 15% fall in FEV1 or a 35% fall in specific airway conductance. Skin responsiveness as indicated by the wheal response to intradermal histamine was also unchanged. We conclude that physiologic changes in hormone levels during the menstrual cycle are not in themselves associated with changes in airway or skin responsiveness to histamine.