Cayman’s Glycolysis Cell-Based Assay Kit provides a colorimetric method for detecting extracellular L-lactate, the end product of glycolysis, in cultured cells. In the assay, lactate dehydrogenase catalyzes the oxidation of lactate to pyruvate, in which the formed NADH reduces a tetrazolium substrate (INT) to a highly-colored formazan which absorbs strongly at 490-520 nm. The amount of formazan produced is proportional to the amount of lactate released into the culture medium and can be used as an indicator of the cellular glycolytic rate. This assay can be adapted to high-throughput screening for glycolysis regulators at the cellular level. Furthermore, the non-invasive sampling leaves the cells intact and thus allows multiplex testing for additional markers.