N-Decanoyl p-nitroaniline (DepNA) is a nitroaniline fatty acid amide used to measure fatty acid amide hydrolase (FAAH) activity. FAAH, which accepts various amide head groups beyond the ethanolamine of its endogenous substrate anandamide (AEA), can hydrolyze fatty acid amides with fewer carbons and fewer double bonds than arachidonate. When exposed to FAAH activity, DepNA releases the yellow colorimetric dye p-nitroaniline (ε = 13,500 at 410 nm), enabling fast and convenient FAAH activity measurement using a 96-well plate spectrophotometer.