Neurotoxic damage of central serotonergic systems has been demonstrated in numerous animal studies after exposure to methylenedioxyamphetamines (ecstasy). A high intensity dependence of auditory evoked potentials and, particularly, of the tangential N1/P2 source activity has been associated with low levels of serotonergic neurotransmission in humans. We performed an auditory evoked potentials study in 28 abstinent recreational ecstasy users and two equally sized groups of cannabis users and nonusers. The ecstasy users exhibited an increase of the amplitude of the tangential N1/P2 source activity with higher stimulus intensities; whereas, both control groups failed to exhibit this feature. These data are in line with the hypothesis that abstinent ecstasy users present with diminished central serotonergic activity. This feature of information processing is probably related to the well-recognized neurotoxic potential of ecstasy. Our data indicate that recreational ecstasy use may cause long-term alterations in the function (and possibly structure) of the human brain.