Background: Chronic rhinosinusitis with nasal polyps (CRSwNP) is a common disease with an uncertain pathophysiology. It is characterized by polyps rich in eosinophils, with an activation status already investigated at the tissue level. In a group of CRSwNP patients, we assessed the activation status of circulating eosinophils in the blood before migration into tissues. Methods: Thirteen patients with CRSwNP and 16 healthy volunteers were enrolled. Several biologic parameters were studied: blood count of eosinophils; plasma eosinophil cationic protein; oxidative metabolism by chemiluminescence at baseline or when activated by phorbol 12-myristate 13-acetate or platelet-activating factor, with or without interleukin-5 (IL-5); percent of granulosar cells; and mean fluorescence intensity (MFI) by flow cytometry. Results: The mean number of eosinophils was significantly higher in patients with CRSwNP, whose eosinophils showed increased oxidative metabolism in the basal or activated state significantly decreasing in the presence of IL-5. There was also a higher percentage of CD49d(+), CD25(+), and CCR3(+) cells in patients, and a nonsignificant decrease in descending order in MFI between the control group, patients with normal eosinophil levels, patients with hyper-eosinophilia, and patients with aspirin-exacerbated respiratory disease. Conclusion: This study demonstrates a priming state of circulating eosinophils in CRSwNP patients when compared with healthy controls, as evidenced by the extent of oxidative metabolism, with increased sensitivity to IL-5 and by the observed variations of percent and MFI of CD49d, CCR3, and CD25. This priming is thus found at the peripheral level and occurs before the migration of eosinophils to polyps, reflecting the systemic and not just local nature of abnormalities in CRSwNP.