Vascular endothelial growth factor (VEGF) is known to play a central role in tumour angiogenesis. Up to now inconclusive data have been published on the clinical-biological significance of circulating VEGF and on the most suitable blood fraction for measuring it. The aims of this pilot study were to assess VEGF in blood compartments of 16 healthy control volunteers and 56 gastrointestinal cancer patients, prospectively collected, to identify the most suitable blood fraction for the determination of VEGF and to evaluate its possible clinical-biological significance. Samples of serum (S) and plasma (P) in both sodium citrate (SC) and sodium citrate-theophylline-adenosine-dipyridamole (CTAD) were collected from venous blood. After the centrifugation and separation methods VEGF levels were detected by ELISA in: S, plasma-platelets poor (P-PP), plasma-activated platelets rich (P-APR) and blood-lysed whole (B-LW). The best differentiation between healthy control volunteers and cancer patients in VEGF level was seen for P-APRCTAD (mean value: 278 pg/ml vs 77 pg/ml; p=0.0036 by t-test). No significant correlation among the blood fractions of VEGF analysed and clinical-pathological features was found. Our data suggest that P-APRCTAD blood fraction, obtained according to well standardised conditions, could represent the most suitable compartment for the assessment of VEGF. We suggest that VEGF levels in P-APRCTAD could play a role as an angiogenic marker of malignant gastrointestinal transformation. Further studies on a larger series of patients and healthy controls with the same experimental methodological conditions are required to confirm our preliminary conclusions.