L(+)-Lactate is the major stereoisomer of lactate formed in human intermediary metabolism. The lactate to pyruvate ratio reflects the redox state of the cell and describes the balance between NAD+ and NADH, which is dependent on the interconversion of lactate and pyruvate via lactate dehydrogenase (LDH). Monitoring lactate levels is, therefore, a good way to evaluate the balance between tissue oxygen demand and utilization and is useful when studying cellular and animal physiology. Cayman’s L-Lactate Assay provides a fluorescence-based method for detecting L-lactate in biological samples such as serum, plasma, blood, urine, and saliva. It can also be utilized to determine intracellular and extracellular lactate concentrations in cell culture samples. In the assay, lactate dehydrogenase catalyzes the oxidation of lactate to pyruvate, along with the concomitant reduction of NAD+ to NADH. NADH reacts with the fluorescent substrate to yield a highly fluorescent product. The fluorescent product is analyzed with an excitation wavelength of 530-540 nm and an emission wavelength of 585-595 nm.