In the present study the ultrastructural aspects of the migration of polymorphonuclear leukocytes (PMN) in apparently normal skin following the epicutaneous application of leukotriene B4 (LTB4) were studied and it was investigated whether this model is representative of the migration of PMN in psoriatic skin. At the ultrastructural level the following features were observed: degranulation of PMN, formation of fenestrations and gaps of the endothelium, a multilayered basal lamina and hyperactive endothelial cells with protrusions and focal necrosis of these cells. Epicutaneous application of LTB4 is a practical approach to study the dynamics of the interaction between PMN and the endothelium in vivo.