Methylenedioxy-N-methylamphetamine (MDMA, "Ecstasy") and other related phenylethylamines are nowadays used extensively in Western Switzerland at dance clubs and raves. There is a widely held belief among teenagers and misusers that ecstasy is safe. In the last years however, an increasing number of reports of MDMA-related deaths has been reported. Acute clinical toxicity problems following MDMA ingestion include hyperthermia, convulsions and arrhythmias. There is also growing concern that these phenylethylamines are neurotoxic and cause long-term damage to serotonineric nerve terminals in animal brains. Qualitative analyses by GC-MS of street samples of ecstasy showed that only a part of them contain MDMA or related phenylethylamines (MDA, MDEA, MBDB and 2C-B). Most of them were mixed with caffeine and an excipient (sugars or polyols [e.g. mannitol]). Amphetamine cut with caffeine and other drugs (e.g. testosterone), stimulants (e.g. pseudoephedrine) and other drugs unrelated to stimulants and phenylethylamines (e.g. LSD, chloroquine, vasodilators) were also detected. Quantitative determinations performed by HPLC-DAD or EC-DAD reveal huge fluctuations in the amount of active substance(s) per tablet. MDMA and related compounds display unique psychoactive properties, acting as a stimulant and inducing feelings of empathy. The effects of MDMA intake are very likely the results of the large release of serotonin (5-HT) in the synaptic cleft, of the inhibition of the re-uptake inactivation of 5-HT and of the inhibition of a key-enzyme involved in the biosynthesis of 5-HT. Forensic investigations performed at our institute showed significant blood levels of MDMA, MDEA and MDA in samples drawn from people suspected of driving under the influence of psychoactive drugs. Up to now, no death could be attributed to MDMA intoxication only because our analyses always revealed the additional presence of toxic amounts of other psychoactive drugs (e.g. opiates, cocaine). Our study shows that because of the variable composition of ecstasy tablets, unpredictable types and amounts of drugs may be taken by MDMA misusers. Moreover, there is considerable concern that traffic accidents may be caused by MDMA-abusers. MDMA intake could result in severe intoxication and even death, especially when combined with other types of drugs.