The explorative and evaluative study had more than 1,000 participants. Following preliminary research, information was collected by means of a survey of partygoers at the start and end of 10 large house parties, observations at 28 house parties and 24 clubs and discotheques, interviews of 47 former ecstasy users, interviews of 10 informants, and questionnaire responses from 197 additional party and club visitors. About 30 percent of the partygoers were female, the average age was under 21 years, and 54 percent visited a house party at least once a month. Parties were generally held in locations such as exhibition and sports halls, skating stadiums, and sheds or hangars. Services at the parties included security, the Safe House Campaign, and first-aid workers. Parties generally lasted from early evening until dawn. Licit and illicit drugs had an important role. Sixty-four percent of the participants consumed ecstasy, and 34 percent consumed amphetamines at the party; only 34 percent drank alcohol at the party. The parties had a friendly atmosphere; the majority of participants reported no health problems at the end. Findings indicated that the conditions at house parties had little or no negative effect on the well-being of partygoers and that relatively few partygoers were at risk for health problems even in the short-term; one proviso related to this conclusion is the continuation of the recommendations of the Memorandum City Hall and House. 13 references (Author abstract modified)