The peripheral inflammatory response, as a proxy for the acute-phase response (a known mechanism for ischemic preconditioning), and non-damage-producing transient ischemia must exist together in humans if this candidate mechanism confers ischemic tolerance. The present study was aimed at determining whether the peripheral inflammatory response (ie, elevated white blood cell, neutrophil, and monocyte counts) exists in transient ischemic attack (TIA) and stroke patients at the time of emergency room admission. The null hypothesis was tested for the variables of the peripheral inflammatory response between the mean of the laboratory normal population versus stroke and TIA patients. A retrospective review of 1041 medical records yielded 12 first-time TIA patients and 34 first-time stroke patients with no confounding evidence of other inflammatory processes. In both groups, neutrophil and monocyte percentages were significantly higher than the laboratory means (in TIA cases: neutrophils, 67.9% [12.67%], P = .001; monocytes, 8.2% [2.7%], P = .020; in stroke cases: neutrophils, 64.9% [9.1%], monocytes, 7.7% [1.6%]; both P < .001). Absolute neutrophil count was significantly higher than the laboratory mean for the stroke cases (5.13 [1.88] K/UL; P = .022). Lymphocyte percentages and absolute lymphocyte count in both groups were significantly and abnormally lower than the laboratory mean (in TIA cases, 21.7% [10.5%] and 1.4 [0.6] K/UL, respectively; in stroke cases, 24.7% [8.4%] and 1.9 [0.7] K/UL, respectively; all P <or= .001). No other absolute counts were significant. These findings suggest that the peripheral inflammatory response exists in transient ischemia, which hypothetically does not damage brain tissue, as well as in stroke (or permanent ischemia), which is known to produce brain tissue damage.