3,4-Methylenedioxymethamphetamine (MDMA), one of the most popular illicit recreational drugs, is metabolized primarily into 4-hydroxy-3-methoxymethamphetamine (HMMA) by drug-metabolizing enzymes. HMMA is further metabolized by phase II enzymes to give the glucuronide or sulfate which is excreted into urine. In the present study, enzyme kinetic studies with various microsomes showed that rat liver microsomes pretreated with Aroclor 1254 were most suitable for the enzyme-assisted synthesis of the glucuronide (HMMA-Gluc). This method selectively produced the beta-anomer of HMMA-Gluc in a very high, isolated yield (71%), and with a purity that was sufficient for use in an analysis of MDMA intake and for enzyme kinetic studies. We also identified, by an LC-MS method, the human uridine 5'-diphosphate-glucuronosyltransferase (UGT) isoforms that catalyze the glucuronidation of HMMA. Among 12 isoforms of human recombinant UGT expressed in insect cells, UGT2B15 was the only isoform that showed adequate enzymatic activity in catalyzing HMMA glucuronidation with K(m) and V(max) values of 3.8 mM and 1.6 nmol/min/mg protein, respectively. The finding that UGT2B15 is capable of HMMA glucuronidation suggests this isoform may have an important in vivo role in human MDMA metabolism.