The JORUM underground nuclear explosion, September 16, 1969, at the Nevada Test Site, induced a series of short- and long-duration stress changes in the nearby rock. These changes were monitored with solid-inclusion three-dimensional probes that were emplaced in drill holes at four locations. The stress in the nearby rock mass stabilized within 2 weeks after the explosion but in all instances a relatively more tensile stress equilibrium was reached. The stress-change directions resulting from the explosion were closely aligned with prominent fault and joint-system trends. There was good agreement of changes in stress magnitude and direction with postshot seismic activity, alignment of after-shock epicenters, and structural directions. The relationship between geological features, seismic activity, and stress changes strongly suggests that the explosiontriggered release of stored tectonic strain energy is controlled by pre-existing geological conditions.