A human malignant fibrous histiocytoma (MFH) cell line, designated as MFH-ino, was established from the maxillary tumor of a 45-year-old woman. Clinically, the original tumor was accompanied by extensive destruction of the surrounding tissues. Cells were obtained from the explant culture of tumor fragments. Both histiocytic and fibroblastic markers were observed in the histochemical and immunocytochemical studies of MFH-ino. The cells were positive for lysozyme, alpha-1-antichymotrypsin, and the collagen types I, III, IV, V, but were negative for alpha-1-antitrypsin, acetate esterase and type II collagen. As biochemical examinations of the culture cells, collagen synthesis was assayed by the measurement of hydroxyproline and the content increase in culture dishes with time after cell inoculation. Collagenase activity secreted in culture medium was also examined with FITC-labeled type I collagen as substrate, and high activity was detected at the late stage of the stationary phase. Further, the MFH-ino cells had high acid phosphatase activity while lacking alkaline phosphatase activity. These findings indicated that MFH-ino cells expressed the various properties of MFH, which will be of importance for understanding the biological behavior, and especially the collagen metabolism, of MFH.