The effect of brain damage on body temperature rhythm was investigated by spectral analysis using the maximum entropy method. The rectal temperatures of 56 patients with acute stroke were recorded for 1-3 days by actigraphy. Many patients with disturbance of consciousness showed infradian rhythm. Ambulatory patients tended to have circadian rhythm, and non- ambulatory patients tended to show infradian rhythm. The study's findings suggest that impaired physical activity and disturbance of consciousness affect body temperature rhythm in patients with acute stroke.