Some authors have suggested that psychological stress induces the production of reactive oxygen species (ROS). Some studies have supported that bilirubin exerts anti-oxidative effects in vivo. However. it is not known whether ROS induced by psychological stress provoke bilirubin oxidation in vivo. We investigated if the concentration of bilirubin oxidative metabolite (BOM). a bilirubin oxidative metabolite, increased in urine from subjects exposed to psychological stress. Sixty, healthy male volunteers Working in a pharmaceutical company were divided into a Group I which did not attend a conference, a Group II which attended a conference but did not deliver a speech. and a Group III which attended a conference and delivered speeches in the presence of the company executives. Subjective stress was scored (self-rating score) after subjects in Group III delivered their speeches at the conference. Urine was collected on the next day. The BOM concentrations, These measured by enzyme-linked immunosorbent assay, were normalized to the urinary concentration of creatinine. The concentration of BOM in Group III was significantly higher compared to that in Groups I and II (p < 0.01 and p < 0.05. respectively). Furthermore. in Group III. the concentration of BOM correlated with the self-rating stress score (r = 0.53 p < 0.01). These findings suggest that emotional stimuli are associated with an increase in the oxidative metabolites of bilirubin in human urine, and that BOMs could be useful markers of psychological stress. (C) 2002 Elsevier Science (USA). All rights reserved.