Expression and pathological relevance of inducible nitric oxide synthase in osteosarcoma of the jaws. The aim of the present study was to examine the expression of inducible nitric oxide synthase (iNOS) in osteosarcoma of the jaw, and its relationship with tumour angiogenesis and clinicopathological characteristics. Streptavidin peroxidase immunohistochemical staining was used to detect the expression level of iNOS and CD34 in paraffin-embedded samples from 25 patients. Osteosarcoma of the jaw was associated with overexpression of iNOS, which correlated with tumour microvessel density (MVD). iNOS expression correlated with the size, pathological grade and clinical stage of the osteosarcoma, and also with clinicopathological characteristics such as primary occurrence or recurrence of tumours. There was no correlation with metastasis. iNOS may promote tumour angiogenesis in osteosarcoma of the jaw, and so may represent an important target in anti-tumour therapy.