Abnormally high blood levels of vascular endothelial growth factor (VEGF) appear to be associated with a poor prognosis in advanced cancer, probably as a consequence of its angiogenic and immunosuppressive effects. The prognostic significance of changes in VEGF secretion during cancer chemotherapy is still unknown. This study aimed to investigate the relation between VEGF variations and therapeutic results during chemotherapy in advanced malignancies. The study included 90 metastatic cancer patients, 59 with non-small cell lung cancer and 31 with colorectal carcinoma. Chemotherapy consisted of cisplatin plus etoposide for NSCLC and camptothecin for colorectal cancer. Abnormally high (> 2 SD with respect to values in healthy controls) pretreatment VEGF levels were found in 38/90 (42%) patients. The percentage of non-progressive disease in response to chemotherapy was significantly higher in patients with normal levels of VEGF prior to therapy than in those with elevated pretreatment values of VEGF (10/32 vs 4/27; p < 0.05). Moreover, the percentage of VEGF level normalization during chemotherapy was significantly higher in patients with objective tumor response or stable disease than in progressing patients (10/18 vs 0/20; p < 0.001). Finally, among patients with tumor response or disease stabilization, the one-year survival rate was significantly higher in patients with chemotherapy-induced normalization of VEGF than in those with persistently high VEGF blood levels (9/10 vs 3/8; p < 0.05). These results suggest that changes in VEGF levels during chemotherapy may represent a useful biomarker to predict the effect of chemotherapy in terms of tumor response and survival in patients with metastatic solid neoplasms.