The significance of neovascularization for tumor growth and metastasis has recently been postulated for human cancers; increased microvessel density correlates with increased frequency of metastasis. In the present study, micro-vessel density was examined in 42 cases of malignant fibrous histiocytoma (MFH). Microvessels were defined as lumens surrounded by anti-factor-VIII-related antigen (FVIII-RA)-antibody-stained endothelium, and counted in a × 400 field. The number of microvessels varied from 4 to 79 (median 14.5). When cases were divided into groups with less than or greater than 20 micro-vessels, there were no prominent differences in age distribution, sex ratio, size of tumor, depth of tumor, and histologic subtypes between the two groups. The number of microvessels in 19 cases with and 22 cases without metastasis was 19.4 ± 14.9 and 19.6 ± 17.4, respectively. Angiogenesis is apparently not a key factor in the formation of metastasis by M