This study was performed to determine normal physiological fluctuation of serum progesterone Hormone on peak Expiratory Flow Rate (PEFR %). The study involved 50 healthy in follicular phase (group A) and 59 healthy premenopausal women in luteal phase (group B). PEFR % was higher in luteal phase in compared to follicular phase of premenopausal women, the relationship was significant (p<0.01, r= 0.992).Serum progesterone level was higher in luteal phasein compared to follicular phase of premenopausal women (P<0.05). There were a significant positive correlation between PEFR % and progesterone level in group A (P<0.01, r= 0.859)) and group B )p< 0.01, r= 0.995).Therefore, the normal cyclical progesterone hormone level should took considerably in interpretation of PEFR% . Keyword: progesterone Hormone, peak Expiratory Flow Rate, follicular phase, luteal phas
