The eccrine porocarcinoma is a rare adnexal tumor of human skin. It has been related to the acrosyringeum of the sweat gland. An immunohistochemical study on paraffin sections of eight porocarcinomas and a control group of 29 poromas was conducted to investigate the differentiation of porocarcinomas. Antibodies against (neuro-) glandular antigens and selected intermediate filaments were used for indirect immunoperoxidase staining with amino ethyl carbazole. Porocarcinomas disclosed variable amounts of cells labeled with CEA, S100A, LS59, NKI/C-3, Cam 5.2, Vim9(1), and wide spectrum keratin. Cellular phenotypes showed greater variability than the benign poromas. The immunostaining patterns of porocarcinomas suggest a differentiation program towards inner duct cells and myoepithelium thereby questioning their classification as acrosyringeal neoplasms.