URB754 is a potent and noncompetitive inhibitor of monoacylglycerol lipase (MAGL), exhibiting an IC50 value of 200 nM for the recombinant rat brain enzyme. However, it does not inhibit human recombinant, rat brain, or mouse brain MAGL at concentrations up to 100 µM. There is evidence that the MAGL inhibitory activity of URB754 may be attributed to the impurity bis(methylthio)mercurane (IC50 = 11.9 nM for rat recombinant MAGL) that is found in commercial preparations. URB754 inhibits rat brain fatty acyl amide hydrolase (FAAH) with an IC50 value of 32 µM and binds weakly to the rat central cannabinoid (CB1) receptor with an IC50 value of 3.8 µM. It does not inhibit COX-1 or COX-2 at concentrations up to 100 µM. Inhibition of MAGL hydrolysis of 2-arachidonoyl glycerol (2-AG) is associated with enhanced stress-induced analgesia and may represent a novel drug target in pain and stress management.