Vascular endothelial growth factor (VEGF), acidic and basic fibroblast growth factors (FGF-1 and -2), and transforming growth factor (TGF ) are potent angiogenic cytokines. Malignant mesothelioma of the pleura presents with a high intra-tumoural microvascular density (IMD) which also has prognostic relevance. This study was designed to verify the immunohistochemical expression of the angiogenic cytokines in mesothelioma as well as in non-neoplastic human mesothelial cells and to study the individual as well as the combined expression of these cytokines in mesothelioma in relation to both IMD and prognosis. In addition, four mesothelioma cell lines were studied by ELISA for the secretion of VEGF and FGF-2 in their supernatants and were shown to contain high levels of both of these cytokines. Immunohistochemically, VEGF, FGF-1 and -2, and TGF immunoreactivity was present in 81, 67, 92 and 96 per cent of mesotheliomas, and in 20, 50, 40, and 10 per cent of samples of the non-neoplastic mesothelium, respectively. Co-ordinate expression of the cytokines was observed whereby mesotheliomas expressed more than one cytokine. The combined immunohistochemical expression levels for all four cytokines correlated significantly with both IMD (p=0β’01) and prognosis (p=0β’0013). When studied individually, high FGF-2 expression correlated best with more tumour aggressiveness and worse prognosis for mesothelioma (p=0β’0011). There was no significant correlation between prognosis and immunoexpression of VEGF (p=0β’07), FGF-1 (p=0β’3), or TGF (p=0β’1), or between IMD and any of the cytokines studied individually. These data support the assertion that selective angiogenic cytokines might contribute to the progressive changes of mesothelioma by tumour angiogenesis.