The circadian rhythm of serum prolactin was determined in 12 patients with seizures, and 28 age- and sex-matched healthy subjects (14 men and 14 women). Blood was also collected every 15 min for 2 h immediately after a simultaneously video/EEG-documented epileptic (6 patients) and psychogenic seizure (5 patients) for the determination of prolactin, thyrotropin, growth hormone, cortisol, melatonin, catecholamines and serotonin. During the seizure-free interval, the circadian profile of serum prolactin was lower in female patients than in healthy women. Serum prolactin, thyrotropin, growth hormone, and cortisol were increased postictally, followed by a decrease, after a grand mal or complex partial seizure, but not after a psychogenic seizure in comparison to baseline serum hormone levels obtained during the same time on a seizure-free day. During the seizure and for 2 h afterwards, blood serotonin, serum melatonin, dopamine, and epinephrine did not alter and were within the reference limits of healthy subjects. Serum norepinephrine was lower in patients compared to healthy subjects (p less than 0.05). The simultaneous elevation of serum prolactin, thyrotropin, growth hormone, and cortisol points to a central stimulation of the hypothalamic-pituitary axis during an epileptic seizure, but not during seizures of psychogenic origin.