This study examined the characteristics of gay men attending circuit parties and their drug use. In particular, the role of methylenediomethamphetamine (MDMA, "ecstasy") was considered in relation to other drug use and sexual behavior. A one-page survey was distributed to 173 men attending a circuit party. Respondents were generally gay men, Caucasian, employed, and well-educated. Twenty-five percent self-identified as HIV-positive. Eighty-six percent reported using at least one substance on the day of the party; polydrug use was frequent. The most common substances were MDMA, ketamine, and methamphetamine. MDMA use was highly associated with ketamine, methamphetamine, and cocaine use. MDMA use was also associated with significantly more receptive anal intercourse. Circuit parties are settings of increased drug use and associated high-risk sexual behavior. A better understanding of these issues is needed to develop interventions aimed at reducing drug use and sexual risk taking among gay men who attend circuit parties.