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P(論文), Histatin-5 and the basic Proline-rich peptide P-E (PRP-PE) have been revealed as candidates of bitter binding proteins. However, it has not been confirmed whether these compounds were carriers of or blockers to bitter taste so far. On the other hand, it has been reported that psychical stress reduced the sensitivity of bitterness. The present study was carried out to measure the clinical concentrations of Histatin-5 and PRP-PE in saliva under the mental stress. Stimulated parotid saliva was obtained from the parotid glands of 10 healthy adult subjects before and after the load of stress of the Kraepelin psycho-diagnostic test with a loud noise (5,000Hz, 100dB) for 30 mins. The salivary cortisol concentration and the LF/HF ratio on ECG were adopted as indices of sympathetic nervous activity to check a liability for the load of stress. The concentrations of Histatin-5 and PRP-PE in saliva were quantified by ELISA test. A significant increase in the salivary cortisol after the stress was recognized in half of the subjects, among which an increase of LF/HF ratio was also observed. Histatin-5 in the parotid saliva was significantly reduced by the stress in this group, but PRP-PE was not. These findings suggest that Histatin-5 in saliva might be a carrier protein of bitter substances, but a function of PRP-PE was not clear in this study.