The serotonergic deficits induced by 3,4-methylenedioxyethamphetamine (MDEA, "eve"), were examined and compared with 3,4 methylenedioxymethamphetamine (MDMA, "ecstasy"). A single dose of MDEA (10, 20, or 40 mg/kg IP) induced a dose-related hyperthermia, but only the highest dose significantly reduced 5-HT content and 5-HT transporter density in the frontal cortex and in the hippocampus 7 days later. Long-term serotonergic deficits were much more marked when MDEA was given repeatedly (40 mg/kg IP., b.i.d., for 4 consecutive days). Single or repeated administration of MDEA induced no change on 5-HT1A receptor density in the frontal cortex, brain stem, or hippocampus, although 3 h after both treatments plasma corticosterone levels were significantly increased. MDEA (5-20 mg/kg, IP) produced significant retention deficits in a passive-avoidance learning task. Conversely, 7 days after the repeated administration of MDEA (40 mg/kg b.i.d., for 4 consecutive days) no effect on passive-avoidance performance was observed unless rats were treated again with another dose of MDEA (20 mg/kg IP) 30 min before the training trial. The 5-HT1A receptor antagonist, WAY 100635, prevented the impairment in retention performance induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), but not by MDEA or MDMA, indicating that the effect of these amphetamine derivates was not mediated by 5-HT1A receptor activation. The results suggest the risk of serotonergic dysfunction associated with MDEA abuse in humans.