Aldehyde dehydrogenase (ALDH) is known to be susceptible to oxidation, and its assays require stabilization of the enzyme by thiols. Application of the fluorimetric method to assay the ALDH activity in human saliva demonstrated significant differences between procedures utilizing glutathione (GSH) and dithiothreitol (DTT) as stabilizing agents. It has been recently shown that average aldehyde dehydrogenase (ALDH3A1) activity in cancerous (oral cavity cancer) patients' tissues was higher than that found in the control group, what may indicate induction of tumor-specific ALDH.