Aldehyde dehydrogenases (ALDHs) represent a group of enzymes that oxidize a wide range of endogenous and exogenous aldehydes to their corresponding carboxylic acids, which affect both developmental and toxicological functions. Pharmacological inhibitors or activators of ALDH activity have been developed to examine the metabolism of alcohol as well as a number of pathological conditions, including cancer, Type II hyperprolinemia, Sjögren-Larsson Syndrome, Parkinson’s Disease, Cardiac Disease, and hyperammonemia. Cayman’s Aldehyde Dehydrogenase Assay provides a fluorescence-based method for detecting ALDH activity in tissue homogenates, cell culture samples, and purified ALDH preparations. In the assay, ALDH catalyzes the oxidation of acetaldehyde to acetic acid, along with the concomitant reduction of NAD+ to NADH. NADH reacts with the fluorometric developer to yield a highly fluorescent product which can be analyzed with an excitation wavelength of 530-540 nm and an emission wavelength of 585-595 nm.