Angiogenesis is an important part of normal and pathological processes, including tumour growth, metastasis, inflammation and wound healing. VEGF is the best known angiogenic factor, implicated in tumour-associated microvascular hyperpermeability and carcinogenesis. We investigated 103 malignant pleural mesotheliomas, analysing the expression of vascular endothelial growth factor using immunohistochemistry and in situ hybridization. The grade of microvessel density was assessed with the aid of anti-factor-VIII antibodies. An increased expression of VEGF was found in biphasic and epithelioid mesotheliomas, correlating in a statistically significant manner (P<0.042). In situ hybridization confirmed the specificity of VEGF mRNA expression. There was a robust correlation between VEGF expression and increased microvessel density (P<0.001), and positive mesotheliomas had significantly higher microvessel densities than negative specimens. There was also a significant correlation between microvessel density and histological pattern. As growth pattern tended towards biphasic and sarcomatoid mesotheliomas the density of micovessels decreased (P<0.05).