This report describes and examines a case series of seven ecstasy-related visits to the emergency room, measuring plasma MDMA levels in each case. All individuals had taken ecstasy at the same London-area nightclub. The series includes two fatalities, one severe adverse event, and four cases of mild to moderate adverse events. Cases included a fatality in a 20 year old man who experienced hyperthermia and cardiac arrest (2 mg/L blood MDMA), and a fatality in a 22-year old man after a fall from a glass roof, hyperthermia, and deteriorating hepatic and renal function (0.93 mg/L blood MDMA). The third severe adverse event occurred in an 18 year old man who had collapsed outside the nightclub, and who was hyperthermic and showed signs of agitation on arrival (0.35 mg/L blood MDMA), with recovery occurring over 72 h. Case 3 showed signs of rhabdomyolysis. Since Case 3 also developed a urinary tract infection, it is uncertain whether hyperthermia arose solely from ecstasy use. Amount of ecstasy consumed is unknown in both fatalities, but the third case reported taking 5 tablets plus 1 g "speed"; (MDMA was detected in the "speed" powder). Cooling procedures were performed on all 3 cases of hyperthermia, including cooled intravenous fluid and ice packs. Dantrolene was used in Case 3. Cases 4 through 7 consisted of 3 men and 1 woman, ages 17-23, with blood MDMA levels ranging from 0.1 to 0.25 mg/L, reporting a consumption of between 1 to 4 ecstasy tablets. Reasons for presenting at the emergency room are not listed, though Case 5 (18-year old man, blood MDMA 0.23 mg/L, took 4 tablets) reported being anxious, and Case 4 23-year old man, blood MDMA 0.25 mg/L, took 2 tablets) had mildly elevated body temperature (37.6 C). Serum was negative for barbiturates, benzodiazepines, cannabis, cocaine or opiates in all cases, and 0.12 mg/L amphetamine was detected in Case 3. A tablet supplied by a patient was found to contain an unspecified amount of MDMA. No other substances or contaminants were detected in the tablet, or in serum. However, it is not entirely clear whether the authors tested for all possible tablet contaminants, such as dextromethorphan or PMA. In this case series, blood MDMA level was associated with severity of adverse event. This is the first case series describing adverse events after ecstasy ingestion occurring in the same location. Nightclub temperature was not assessed but was assumed to be warm; ambient outdoor temperature on the night of all adverse events was reported as 13.2 to 17.8 deg C (55.8 to 64 deg F) . The authors assume that all individuals took the same ecstasy "brand" without confirming this through tablet analysis, raising the possibility that number of tablets taken cannot be considered an indirect measure of dosage. This report would have been more informative if the four mild to moderate adverse events were described in more detail. It is important to note that severe adverse events do not always occur with high plasma MDMA levels (see Baggott et al. 2001), and that other factors, such as pre-existing health and level of exercise, may also be associated with ecstasy-related adverse events. It may be that assessing adverse events arising in the same setting or location increases the visibility of this relationship.