Morphological, enzyme histochemical and immunohistochemical studies were carried out from the tissues obtained from 5 cases of sacral decubital ulcer (granulation tissue) and 7 cases of malignant fibrous histiocytoma (MFH). In the granulation tissues short spindle shaped or elliptical cells other than histiocyte were found as well as typical elongated fibroblast. Electron-microscopically these short spindle shaped or elliptical cells has many dendritic, fragmented rough endoplasmic reticula, a plenty of free ribosomes, some small mitochondria, an oval, elliptical or irregular shaped nucleus, a or two prominent nucleoli, and often a few dense bodies, but had not the specific characteristics of histiocyte, including pseudopodia, multivesicular bodies and phagosomes. Further, they were positive for acid phosphatase (AcP) and esterase enzyme histochemically, and ferritin (Fer), α1-antitrypsin (AT), α1-antichymotrypsin (ACT), fibronectin (FN), HLA-DR, Leu 10 and OKT 9 immunohistochemically. Consequently, these short spindle shaped and elliptical cells, which we proposed to term “Fibrohistiocytoid cell”, had both the characteristics of fibroblast and histiocyte, and it was probable that they were transformed from typical elongated fibroblast. On the other hand, MFH was composed of two major tumor cell types, fibroblast-like and histiocyte-like cells. Moreover, storiform pattern, which was considered as one of pathognomonic features of MHF, was mainly composed of fibroblast-like cells. If any difference in each case or the sites of tissue sections, tumor cells of MFH were reacted for AcP and esterase enzyme histochemically, and Fer, AT, ACT, FN, HLA-DR, Leu 10 and OKT 9 immunohistochemically. No marked immunostains for Leu M1, Leu M3, Mo1, Mo2 and third complement receptors were found. The similarity between “Fibrohistiocytoid cell” and tumor cells of MFH was found morphologically, enzyme histochemically and immunohistochemically. These results were attractive on consideration of the histogenesis of MFH.