Nonhabituation of the acoustic startle response is used to identify rat subjects with altered alarm responses subsequent to trauma exposure. Subjects (n = 31) were exposed to 30 minutes of intermittent tail shock on 2 days followed by exposure to the apparatus on the third day. Twenty-nine percent of traumatized rats developed nonhabituation of startle over the subsequent 3 weeks of testing. No control rats developed nonhabituation of startle reactions over a similar time period. These data suggest that this system represents a more accurate representation of clinical PTSD than do other animal models.