Abstract： Objective To explore the expression of neutrophil adhesion molecule CD11b,and plasma level of elastase in patients with anaphylactoid purpura during different clinical phases and their correlation with disease activity.Methods A total of 20 patients with anaphylactoid purpura were recruited into this study,along with 20 normal human controls.Two blood samples were collected from each patients at the first visit(active phase)and after 3～5 weeks of treatment(remission phase).The expression of CD11b was measured by flow cytometry in 12 patients and normal controls,and plasma levels of elastase by ELISA in 20 patients and normal controls.Results Increased CD11b expression and elastase level were noted in patients in active phase compared with those in patients in remission phase(3367.25±434.57 vs 2569.33±411.06.13.98±2.05 vs 4.29±0.80.both P＜0.01).No significant difference was found in CD11b expression between patients in remission phase and normal controls(P＞0.05).while the elastase level was higher in patients in remission phase than in normal controls(4.29±0.80 vs 3.67±0.54.P＜0.05).In active phase of anaphylactoid purpura,the expression of CD11b was positively correlated with the plasma level of elastase(r=0.73,P＜0.01),while no correlation was noticed between them in remission phase(r=0.20,P=0.54).Conclusion Peripheral neutrophils are activated in anaphylactoid purpura,which seems to be more obvious in active phase than in remission phase.