We assessed the clinical utility of circulating angiogenic factors as a predictor for tumor angiogenesis in primary lung cancer. Circulating vascular endothelial growth factor (VEGF) and intratumoral VEGF were assessed by enzyme-linked immuno-sorbent assay (ELISA). There was a significant increase in the mean value of both plasma and serum VEGF concentration in primary lung cancer patients (n=97) compared to those of healthy controls (n=59). There was a significant correlation between plasma VEGF levels and microvessel density (MVD), and also between plasma VEGF and intratumoral VEGF levels. Plasma VEGF in patients with lung cancer appears to be a useful indicator of tumor angiogenesis.