A major earthquake (Hanshin-Awaji earthquake) struck Kobe on January 17, 1995. We had a unique opportunity to study the effect of tremendous psychological stress on blood pressure control in 221 hypertensive patients receiving antihypertensive medication. During the 4 weeks after earthquake, on average, the mean blood pressure increased significantly for both 105 patients who were exposed (living in the area of the very severe earthquake) and 116 patients who were not exposed (living in the surrounding area) (+4.2 +/- 1.0 mm Hg, P < .001, and +/- 2.4 +/- 0.7 mm Hg, P < .005, respectively). In the exposed group, the increase in mean blood pressure peaked in the first week (+6.7 +/- 1.6 mm Hg, P < .001), declined thereafter, and returned to the baseline within 6 weeks after the disaster. The earthquake related blood pressure elevation was, however, significantly attenuated (P < .02) in patients receiving beta-blockers compared with those receiving other drugs. The results indicate that acute psychological stress associated with a sudden natural disaster causes blood pressure elevation in treated hypertensive patients, and suggest the beneficial effect of beta-blockers on such a stress-associated high blood pressure.