Sections of lesional skin of 5 patients with leukocytoclastic cutaneous necrotizing vasculitis (CNV) (3 with documented infective etiology and 2 with unknow etiology) and of 5 patients with lymphocytic CNV with unknow etiology were investigated with immunoperoxidase technique. In lymphocytic CNV the dermal infiltrate was mainly constituted of CD3+, CD4+, CD1a+ and CD36+ cells. ICAM-1 and LFA-1 were strongly expressed. In leukocytoclastic CNV the infiltrate was poor of these cells in the early phase of disease, but they increased in the late phase. ICAM-1 and LFA-1 were strongly expressed in the late phase, while gamma/delta T cells and the expression of 72 kD heat shock protein were significantly present only in leukocytoclastic CNV with documented infective etiology. These results seem to suggest the role of a secondary cell-mediated immune response in the late phase of leukocytoclastic CNV, indicating gamma/delta T cells as a possible clue to the infective etiology of CNV.