Background: Leukocytoclastic vasculitis (LV) is characterized by segmental inflammation of small blood vessels, resulting in ischemic damage to the surrounding tissue. It is considered to be related to a type III hypersensitivity reaction, although the exact etiologic mechanism is not clear. Objective: The purpose of this study was to evaluate neutrophil functions in patients with LV in order to understand their role in the pathogenesis of the disease. Methods: Neutrophil functions were examined in 25 LV patients. The patients were divided into two groups: Group A consisted of 14 patients with drug-induced LV and Group B consisted of 11 patients where LV was induced by other factors. Results: Both groups of patients showed significantly reduced chemotaxis and phagocytosis. Superoxide generation was significantly lower (P < 0.001) only in neutrophils from patients in Group A: 5.8 ± 0.5 nmoles O2/106 cells/min compared to 9.08 ± 0.8 nmoles O2/106 cells/min in the controls. Preincubation on normal neutrophils with the patients' sere caused an increase in their superoxide generation in accordance with the high IL-8 levels in these sera. Conclusions: Neutrophil functions were significantly impaired in patients with LV. It is likely that factors present in LV plasma may chronically activate neutrophils, so that they become refractory to further stimulation. Our study showed that neutrophil superoxide generation is low only in drug- induced LV; this test may assist in distinguishing such patients from those with LV induced by other causes.