Serial serum prolactin and cortisol levels were measured in five patients after a grand mal seizure and in four volunteers with simulated seizures. Single levels were measured after a witnessed seizure in 26 patients and in a matched control group. Significant increase in both prolactin and cortisol levels occurred after seizures. The change in cortisol level may reflect a non-specific stress response, but the increase in prolactin levels could not be accounted for on this basis, and probably indicates an alteration in hypothalamic neurotransmitter activity during the seizure. These findings may have clinical value in the diagnosis of epilepsy.