The suppression of cyclical ovarian activity and the creation of constant oestradiol levels in blood by subcutaneous oestradiol implants has been used to treat 24 patients with menstrual migraine for up to five years. Twenty-three patients improved with treatment, 20 (83%) became completely or almost completely headache-free. Regular monthly periods were induced with cyclical oral progestogens. The treatment was not associated with any problems. The results support the concept that oestrogen withdrawal in the late luteal and menstrual phases of the ovarian cycle is the important precipitating factor in menstrual migraine, and such attacks can be prevented by suppressing the hormonal fluctuations associated with the ovarian cycle.