3, 4-methylenedioxymethamphetamine (MDMA, "Ecstasy") is a recreational drug reported to produce a different psychological profile than that of classic hallucinogens and stimulants. It has, therefore, been tentatively classified into a novel pharmacological class termed entactogens. This double-blind placebo-controlled study examined the effects of a typical recreational dose of MDMA (1.7 mg/kg) in 13 MDMA-naïve healthy volunteers. MDMA produced an effective state of enhanced mood, well-being, and increased emotional sensitiveness, little anxiety, but no hallucinations or panic reactions. Mild depersonalization and derealization phenomena occurred together with moderate thought disorder, first signs of loss of body control, and alterations in the meaning of percepts. Subjects also displayed changes in the sense of space and time, heightened sensory awareness, and increased psychomotor drive. MDMA did not impair selective attention as measured by the Stroop test. MDMA increased blood pressure moderately, with the exception of one subject who showed a transient hypertensive reaction. This severe increase in blood pressure indicates that the hypertensive effects of MDMA, even at recreational doses, should not be underestimated, particularly in subjects with latent cardiovascular problems. Most frequent acute somatic complaints during the MDMA challenge were jaw clenching, lack of appetite, impaired gait, and restless legs. Adverse sequelae during the following 24 hours included lack of energy and appetite, feelings of restlessness, insomnia, jaw clenching, occasional difficulty concentrating, and brooding. The present findings are consistent with the hypothesis that MDMA produces a different psychological profile than classic hallucinogens or psychostimulants.