Neutrophil CD64 expression responded to acute stress not to white blood cell or neutrophil activation. Box plots of a) White blood cells (WBC) and Neutrophils, b) C-reactive protein (CRP), c) procalcitonin (PCT), and d) Fc gamma receptor expression on neutrophils (nCD64) in healthy children and in patients with systemic inflammatory response syndrome (SIRS) after Traumatic Brain Injury (TBI), sepsis (S), or severe sepsis (SS). CRP and PCT differed between the septic groups and C (p < 0.001)* and/or TBI groups (p < 0.03)#. In contrast to the WBC and neutrophils, which did not differ among groups, nCD64 differed between septic groups and C or TBI groups (p < 0.001)* and between TBI and C groups (p < 0.02)**. The bold black line in box plots indicates the median per group, the bottom of the box indicates the 25th percentile and the top of the box represents the 75th percentile; the TBI-bars (whiskers) and horizontal lines show minimum and maximum values of the calculated non-outlier values.