The Drug Information and Monitoring System (DIMS) in the Netherlands, is a toxicoepidemiologic monitor of drug markets that was established in 1992. The DIMS was motivated by the rapid increase of Ecstasy use since the end of the 1980's. Its objective is the exchange of information with regards to the compounds of synthetic drugs on the market, identification of potential health risks, and the description of their prevalence and trends. Insights were gained on the Ecstasy market through the weekly testing of more than 100 drug samples, key information of synthetic drug users who delivered drug samples, and personnel who participated in the DIMS network. It was revealed that pills used as Ecstasy may contain a wide variety of compounds. The percentage of samples containing MDMA increased slowly in 1996, but decreased dramatically in 1997. Amphetamines (“speed” and “ice”) and experimental varieties were found in at least one third of the pills. In 1998, the percentage of MDMA pills increased more than ever before. This indicated that consumers preferred the conventional product. The increase in the use of speed was suggested to have been stimulated due to the decrease in MDMA pills in 1997. The DIMS is intended to supply drug policy authorities with the early notice of new synthetic substances appearing on the illicit drugs markets. Glossary and references