The detection and measurement of free thiols (i.e., free cysteine, glutathione, and cysteine residues on proteins) is one of the essential tasks for investigating biological processes and events in many biological systems. Cayman's Thiol Detection provides a simple, reproducible, and sensitive tool for assaying free thiol content in samples (i.e., plasma, serum, tissue homogenates, cell lysates, and urine). The assay utilizes a proprietary fluorometric detector that reacts with thiol groups to emit a strong fluorescent signal which can be detected using excitation wavelengths between 380-390 nm and emission wavelengths between 510-520 nm.