Objective: Free radicals have been implicated in aging, mutagenesis, inflammation and other pathological conditions. We conducted a study to clarify the relation between a pleasant feeling as a psychological eustress and free radical-scavenging capacity (FRSC) in saliva. Methods: Saliva was collected from 27 healthy volunteers. FRSC before, during and after watching a cheerful comical video for 30 min was measured by using 1,1-diphenyl-2-picrylhydrazyl (DPPH). Results: The median values of FRSC (mumol/ml) before, at 10 and 20 min during and after watching the video were 54.5, 66.8, 66.6 and 69.4, respectively. The FRSC values obtained after watching the video were significantly higher than those before watching it (P<.001). When the FRSC before watching was taken as 1, the value for the group that felt "Very good," "Good" or "Ordinary + Dull" while watching the video for 30 min was 1.38, 1.20 or 0.98, respectively (P<.01). Conclusion: Watching a comical video enhanced the FRSC in saliva; in addition, a pleasant feeling boosted it even more. (C) 2004 Elsevier Inc. All rights reserved.