N-Decanoyl p-nitroaniline (DepNA) is one of several nitroaniline fatty acid amides which can be used to measure fatty acid amide hydrolase (FAAH) activity. FAAH is a relatively unselective enzyme in that it accepts a variety of amide head groups other than the ethanolamine of its endogenous substrate anandamide (AEA). It also will hydrolyze fatty acid amides with fewer carbons and fewer double bonds than arachidonate. Exposure of DepNA to FAAH activity results in the release of the yellow colorimetric dye p-nitroaniline (ε = 13,500 at 410 nm). This allows the fast and convenient measurement of FAAH activity using a 96 well plate spectrophotometer.