Decanoyl m-Nitroaniline (DemNA) 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 (arachidonyl ethanolamide; AEA). It also will hydrolyze fatty acid amides with fewer carbons and fewer double bonds than arachidonate. Exposure of DemNA to FAAH activity results in the release of the yellow colorimetric dye m-nitroaniline (ε = 13,500 at 410 nm) This allows the fast and convenient measurement of FAAH activity using a 96 well plate spectrophotometer.