ALDEHYDE DEHYDROGENASES (ALDHs) are a superfamily of oxidoreductases which catalyze the conversion of aldehydes to carboxylic acids. ALDH is crucial in the metabolism of alcohol as alcohol dehydrogenase breaks down ethanol to acetaldehyde. Acetaldehyde, which is toxic to the body, is in turn broken down by ALDH to acetic acid. Imbalances of aldehyde dehydrogenase have been linked to both alcoholism and alcohol sensitivity in people. Inhibitors of the enzyme have been used in cases to treat alcoholism in patients. Cancer stem cell populations also display a heightened activity of ALDH, making ALDH inhibition a promising anti-cancer therapy approach. This Aldehyde Dehydrogenase Inhibitor Screening Kit is based on the enzymatic conversion of acetaldehyde to acetic acid and NADH by ALDH. The formed NADH in turn reduces a formazan reagent into a colored product the absorbance of which, measured at 565 nm, is proportional to the enzyme activity in the reaction. The percent inhibition of a test compound can be determined by comparing the activity of ALDH treated with a test compound to the activity of untreated ALDH.