Housing mice in the presence of small particles of titanium has been shown to reduce stress-responsive behavior via the autonomic nervous system. Here, we examined the effects of nighttime titanium exposure on stress parameters and autonomic nerve activity in office workers with emotional stress. A randomized double-blind, placebo controlled trial was performed in 24 male subjects with desk jobs, who were randomly allocated to spend 5 nights in rooms with or without titanium. The serum concentrations of stress-responsive hormones (cortisol, adrenocorticotropin, and catecholamine) were measured, and profiles of emotional stress were collected to subjectively assess relaxation. Autonomic nerve activity was examined by power spectra analysis of heart rate variability. In psychological tests, factors related to tension (-14.5%, 95% CI=-15.7--2.1), anger (-11.3%, 95% CI=-13.9--0.7), and emotional stress (-28.5%, 95% CI=-30.0--5.3) were significantly decreased by exposure to titanium. The serum level of adrenocorticotropin was gradually elevated throughout the experimental period in the placebo group (day 4, 80.5%, 95% CI=7.1-37.5 vs. before trial) but not the titanium group. Power spectral analysis of R-R interval data showed a significant elevation in the high-frequency power spectral ratio in subjects housed in titanium rooms (days 1-2, 14.3%, 95% CI=4.7-21.9; days 3-4, 26.8%, 95% CI=4.9-38.7; and days 5-6, 24.1%, 95% CI=5.8-34.0 vs. before trial). These results suggest that sleeping in a room containing titanium lowers physiological and psychological stress. Copyright © 2012 Elsevier Inc. All rights reserved.