Neutrophilic urticaria (NU) is a histologically defined entity, but its clinical and pathogenetic aspects are poorly understood. We investigated 22 NU patients whom we identified by examining 118 biopsies of weals. The patients comprised 11 of 20 with acute urticaria, nine of 49 with chronic urticaria, one of 10 with cold urticaria and one of 10 controls undergoing prick tests. Clinically, NU patients had a shorter mean duration of disease than other urticaria patients and significantly increased erythrocyte sedimentation rate and leucocytosis. Histologically, not only neutrophil counts, but to a lesser extent also eosinophil counts and mononuclear cell infiltrates were significantly increased in lesional skin of NU, and there was more marked vasodilatation and endothelial swelling. On immunohistochemistry, increased tumour necrosis factor alpha and interleukin (IL)-3 expression was noted, compared with other urticarias, whereas IL-8 expression was only minor. These data characterize NU as an acute phase urticarial reaction associated with an intense inflammatory infiltrate and marked upregulation of some mast cell-derived cytokines.