Angiogenesis is a recently described prognostic factor in non-small-cell lung cancer. Platelet-derived endothelial cell growth factor (PD-ECGF), shown to be the enzyme thymidine phosphorylase (TP), induces angiogenesis in vitro and in vivo. High intracellular levels of the enzyme are associated with increased chemosensitivity to pyrimidine antimetabolites. PD-ECGF/TP expression was evaluated immunohistochemically in surgically resected specimens from 107 patients with operable non-small-cell lung cancer using the P-GF,44C monoclonal antibody. High expression of PD-ECGF/TP was found in 25% of cases and was associated with high vascular grade (P = 0.01). Fourteen of 32 (44%) high vascular grade tumours showed a positive reactivity for PD-ECGF/TP vs 13/75 (17%) of low/medium vascular grade. Positive expression was observed more frequently in T2-staged cases than in T1 (P = 0.04). While overall survival was not affected (P = 0.09), subset analysis revealed that node-negative patients with positive PD-ECGF/TP expression had a worse prognosis (P = 0.04). The results suggest that PD-ECGF/TP may be an important molecule involved in angiogenesis in non-small-cell lung cancer. Up-regulation of the enzyme defines a more aggressive tumour phenotype in patients with node-negative disease. Assessment of vascular grade and PD-ECGF/TP expression should be taken into account in the design of randomized trials assessing the role of adjuvant chemotherapy in non-small-cell lung cancer.