This investigation was performed to verify a previous hypothesis which correlates the catamenial seizures with the stoppage of progesterone secretion. White rats from a Wistar strain were tested with an electric bell. Thirty-five animals refractory to the acoustic stimulus were selected for the experiment. Each animal received 9 daily injections with progesterone, 5 mgr/day. The animals were tested with the acoustic stimulus after the 5th and the 9th injections, 24 hours after the administration of the last dose. Audiogenic seizures were obtained in 29.4% of the rats tested after 5 injections and in 40.0% of the rats tested after the 9th injection. The increased seizure susceptibility lasted 3-8 days after the hormone withdrawal. In conclusion, the withdrawal of high doses of progesterone exerts a seizure-activating effect.