The density of the serotonin transporter in the plasma membranes of blood platelets was evaluated by labelled paroxetine binding in three different groups. These groups were: normal controls, epileptic patients having undergone a recent seizure (less than 4 days before) and patients who equally recently presented psychogenic non-epileptic seizures (pseudoseizures). Real seizures resulted in a significant decrease of membrane serotonin transporter density. In the instances of pseudoseizures, its membrane density was undistinguishable from that of normal controls. These data lend further support to the idea that down regulation of serotonin transporter may play a homeostatic role in the cessation of epileptic seizures.