Urinary epinephrine and cortisol hormone output in a remote Australian Aboriginal community was on average about twice as high in those individuals measured on a Thursday or Friday as those measured at the beginning of the next week (Monday or Tuesday). Diastolic blood pressure was about 6 mm Hg higher in the Thursday-Friday group, but the difference in mean systolic blood pressure between the day groups does not reach statistical significance. These physiological differences are associated with a marked dichotomy in behavior in the two time periods: on the first 2 days, virtually all adults were involved in intense gambling activity for large stakes, but this was not a feature of the latter period. This behavior pattern occurs on a regular weekly basis. If substantiated by longitudinal studies, this phenomenon may provide an additional link between human behavior and a poor health profile mediated via the physiological consequences of high stress hormone output.