The effects of Anethum graveolens L. (dill) extracts on the female reproductive system were studied in 54 Wistar female rats with regular estrous cycle in six groups. The experimental groups were fed with 0.045 g/kg and 0.45 g/kg of aqueous extract, 0.5 g/kg and 5 g/kg of ethanol extract for 10 days. The sham group was fed with solvent and the controls received no treatment. The estrous cycle changes were determined by daily vaginal smear changes. At the beginning and at the end of the experiment blood samples were provided to determine the blood estradiol and progesterone concentration. The ovaries were prepared histologically and the volume of different follicles was estimated. A significant increase was observed in the duration of the estrous cycle and in the diestrus phase and the progesterone concentration in high dose extract treatment. The stereological study did not reveal any significant changes in the volumes of ovaries, primary, secondary and graafian follicles. Dill can be used either as a regulatory agent of the menstrual cycle for women with irregular cycles or as an antifertility agent. More studies are needed to clarify the properties of this herb. Copyright © 2006 John Wiley & Sons, Ltd.