Ten women with a documented history of catamenial epilepsy underwent a hormonal study to evaluate hypophyseal-gonadal function. Baseline values of luteinizing hormone, follicle-stimulating hormone and prolactin were similar in catamenial seizure patients and in control groups throughout a complete menstrual cycle. Stimulated secretions of the same hypophyseal hormones in catamenial seizure patients overlapped those of the controls. The luteal secretion ratio of progesterone to estradiol was significantly reduced in catamenial seizure patients versus normal controls. In a subgroup of catamenial seizure patients on antiepileptic therapy, luteal progesterone levels were remarkably decreased compared to normal and epileptic controls. These results indicate that catamenial epilepsy is characterized by an imbalance in ovarian steroid secretion and emphasize the need for an endocrinological assessment in these patients.