The polysomnogram (PSG), blood melatonin concentration, rectal temperature, and answers to a self-evaluation questionnaire about the effects of agarwood (jinkoh in Japanese), which has been reported to have sleep-promoting effects were examined. The subjects tested were male medical students, who were free of otorhinolaryngological diseases and were non-smokers. The results of sleep stage and other sleep variables, and those of rectal temperature rhythm and blood melatonin concentrations showed no significant differences between the baseline nights, experimental nights, and recovery nights.