The vascular endothelial growth factor (VEGF) is known to be one of the most important angiogenic factors under both physiological and pathological conditions. The VEGF overexpression by a wide spectrum of neoplastic diseases has suggested an important role of this cytokine in tumor-neovascularization. A method is described for quantification by reverse transcription-polymerase chain reaction (RT-PCR) of VEGF mRNA in non-small cell lung cancer tissues (NSCLC). The method entails addition to the sample of competitor DNA molecules that share the same primer recognition sites as the amplified target, but which can be easily distinguished by gel electrophoresis because of their different lengths (competitive PCR). We analyzed the VEGF mRNA expression level in 34 cases of lung tumor tissues compared to the respective adjacent normal tissues. In 4 out of 34 (11.7%) analyzed couples there was no VEGF mRNA expression, in 8 out of 34 (23.5%) only normal parenchymal tissue was positive for VEGF mRNA expression; in the remaining 22 cases (64. 7%) both normal and tumor tissues showed PCR products for VEGF. In 17 out of these 22 couples (77.2%) a higher number of VEGF mRNA molecules were present in tumor specimens than in the normal counterpart. According to these results, the competitive PCR-method seems to provide a useful tool for the quantitate VEGF expression in order to identify its role in the development of lung cancer.