Fatty acid amide hydrolase (FAAH) is the enzyme responsible for hydrolysis and inactivation of fatty acid amides including anandamide and oleamide. PHOP is a potent FAAH inhibitor, exhibiting Ki values of 0.094 nM and 0.2 nM for the human and rat enzymes, respectively.{8481} Using a proteomics approach, PHOP was screened against the serine hydrolase family of enzymes, of which FAAH is a member. In this assay, PHOP exhibited IC50 values of 1.1 nM, 1.4 nM, and >100 µM for FAAH, triacylglycerol hydrolase (TGH), and an uncharacterized hydrolase (KIAA1363), respectively.{11817} Knowledge of the specificity of PHOP obtained from this experiment should allow for more accurate interpretation of results using this inhibitor in complex environments such as whole cells or animals.