L-Theanine ((gamma)-glutamylethylamide, (gamma)-ethylamino-L-glutamic acid, glutamic acid (gamma)-ethyl amide, or 5-N-ethyl-glutamine) is the major amino acid found in Camellia sinensis, the source of green tea. L-Theanine exhibits positive effects on the immune system responsiveness to infection, increases the production of brain (alpha)-waves, which causes a state of relaxed alertness, and is helpful in reducing some symptoms of schizophrenia. Cayman's L-Theanine Fluorometric Assay provides a simple, reproducible, and sensitive tool for assaying L-Theanine from plasma, serum, and tea. L-Theanine forms a fluorescent complex with the detector in the presence of cyanide, which can be analyzed at an excitation wavelength of 430-440 nm and an emission wavelength of 485-495 nm.