Nine healthy male subjects and recreational users of 3,4-methylenedioxymethamphetamine (MDMA) participated in a study aimed to assess the usefulness of sweat testing for the detection of MDMA after a single 100-mg dose. Sweat was collected for up to 24 h with the PharmChek sweat patches from which drugs were eluted and then analyzed by immunoassay and gas chromatography-mass spectrometry using deuterated internal standards. The usefulness of a rapid onsite test, the Drugwipe immunochemical strip test, was also assessed. In the sweat patches, MDMA was detected as early as 1.5 h after consumption and peaked at 24 h. Intersubject variability was large; peak MDMA concentrations for the same dose varied in magnitude 30-fold. MDMA concentrations ranged between 3.2 and 1326.1 ng/patch. Only traces of the minor metabolite 3,4-methylenedioxyamphetamine were detected. In all subjects, the onsite test with the Drugwipe was positive at 1.5 h (peak time of MDMA plasma concentration). However, few false-negative results (18%) appeared in the first 6 h after administration. Both sweat patch testing and the onsite sweat strip test may find useful application for noninvasive monitoring of MDMA abuse in sweat.