TWENTYNINE PALMS, Calif. (November 20, 2009)--A military experiment underway in California is designed to try to predict who's most at risk for post-traumatic stress disorder.

Earlier this year, a quarterly publication from a national PTSD center found that studies to date looked at only "a narrow band of the potential risk and resilience predictors."

Select Marine and Army units are undergoing a battery of physical and mental tests before deployment including genetic testing, brain imaging and stress exams.

They are followed in war zones and upon their return home.

Similar research is ongoing at the University of Texas at Austin.

Scientists have collected detailed health data from 178 soldiers from Fort Hood who recently returned from Iraq.