BACKGROUND: "Stress" is associated with changes in many systems of the body. The aim was to study the markers of the innate immune system, Serum amyloid A (SAA) and C-reactive protein (CRP), in subjects with and without posttraumatic stress disorder (PTSD). METHODS: Subjects were refugees from Iraq in the age range of 18-48 years who participated in a longitudinal study focusing on life events. Blood samples were taken in the morning and analysed for Serum amyloid A and high sensitivity C-reactive protein (hsCRP). RESULTS: Contrary to expectations, serum SAA and hsCRP were lower in PTSD than in non-PTSD subjects. Levels of SAA and CRP were further inversely correlated with serum DHEA-s, but not with cortisol. In cases with PTSD at baseline, there was an inverse relationship between difference in self-rated symptoms of PTSD and difference in log-transformed SAA-thus increasing PTSD intensity was associated with decreasing SANo such patterns were obvious with regard to CRP. CONCLUSIONS: Changes in the innate immune system, as measured by acute phase proteins of hepatic origin, seem to be a feature of PTSD. Further, the inverse correlation between DHEA-s, which has been shown to be changed in PTSD, and the acute phase proteins is of interest.