NAD exists in an oxidized form, NAD+, as well as a reduced form, NADH. NAD+, the main free form in cells, functions in modulating cellular redox status and by controlling signaling and transcriptional events, making it and related enzymes drug targets for various metabolic disorders. Cayman's NAD+/NADH Cell-Based Assay Kit provides a colorimetric method for measuring intracellular NAD+/NADH in culture cells. In the assay, alcohol dehydrogenase catalyzes the oxidation of alcohol to acetoaldehyde, in which the formed NADH reduces a tetrazolium salt substrate to a highly-colored formazan, which absorbs strongly at 450 nm. The amount of formazan produced is proportional to the amount of NAD+ in the cell lysate and can be used as an indicator of the cellular NAD+ concentration.