Using the critical point concept and extending Bowman's idea of critical earthquake, we develop an intersecting circle method to locate the critical region. A simulation check shows that this method is effective in finding a given critical region. We selected several real cases from New Zealand and China and used this method to find the critical regions before the occurrence of large earthquakes. The result shows that this method is valid for detecting a critical region and the epicenter of mainshock might be in the critical region. ¿ 2001 American Geophysical Union