3,4-Methylenedioxymethamphetamine (MDMA; Ecstasy) is a serotonergic neurotoxin in laboratory animals that has been used for recreational purposes by humans. The subjective effects of this drug were determined in recreational users at a university campus. Of individuals who had admitted to using MDMA recreationally, 100 of 143 agreed to complete a detailed questionnaire concerning the subjective effects of this Schedule I compound. The most common effect of MDMA was a heightened sense of "closeness" with other people (90% of subjects). Tachycardia, dry mouth, bruxism and/or trismus were reported by the majority of users. These effects probably result from the amphetaminelike properties of the drug. Visual hallucinations were reported by 20% of users. Untoward side effects were most common on the day following the use of MDMA, with complaints of muscle aches, fatiguability, depression, and difficulty concentrating noted by 21% to 36% of subjects. Sixty-seven percent of frequent users of the drug (six or more separate doses) reported that the "positive" effects of the drug decreased with successive doses while the "negative" effects increased. Although these observations should be considered preliminary, they represent the first documentation of the subjective effects of MDMA in recreational users and confirm previous reports obtained from patients treated with this drug.