['Several recent studies report that, after allogeneic hematopoietic cell transplantation (allo-HCT), eosinophilia is a favorable factor for transplant outcomes. However, whether the degree of eosinophilia influences transplant outcomes is yet to be established.', 'We studied 144 patients with hematological malignancy who received allo-HCT at our institution. The stem cell sources were bone marrow in 84 patients, peripheral blood stem cells in 32 patients, and cord blood in 28 patients. One hundred and twelve patients underwent myeloablative conditioning and 49 patients had high-risk disease. We performed semi-landmark analysis to examine the influence of eosinophilia.', 'Eosinophilia developed at a median of 47 days after transplantation in 63 patients (44%). The patients with eosinophilia showed significantly better overall survival (OS) and a lower relapse rate at three years, compared to those without eosinophilia (66% vs 55%, p=0.04 and 30% vs 50%, p=0.002). On analysis following division into groups with mild (500-1,500×10(6)/L) and hyper- (>1,500×10(6)/L) eosinophilia, three-year OS and relapse rates were 68% and 65% (p=0.92), and 31% and 28% (p=0.90), respectively. On multivariate analysis, eosinophilia was significantly associated with lower relapse rates [HR: 0.5 (95% CI: 0.3-0.9), p=0.01] and the same trend was preserved in the analysis of the mild and hyper-eosinophilic groups.'] Is eosinophilia , regardless of degree , related to better outcomes after allogeneic hematopoietic stem cell transplantation?