We investigated the impact of new biological prognostic factors is in 28 patients receiving a median of two courses of cisplatin-based chemotherapy with (n = 14) or without (n = 14) radiation and operation for stage IIIB (T4) non-small cell lung cancer (NSCLC). After induction therapy, 5 patients had a complete and 21 a partial response; 2 had a stable disease. A complete resection was made in 26 patients (93%). Five patients (18%) had their primary tumour and involved vestiges completely sterilized. In the remaining 23, the majority of the tumours showed abnormalities in the p53 gene expression (56%), harboured proliferating cells (91%) and induced angiogenesis (91%). Peritumoural blood and lymphatic vessel invasion (PBLVI) by tumour emboli was observed in 6 tumours. With a median follow-up of 25 months, overall 3-year survival was 48%; disease-free survival (DFS) has not been reached yet. The only significant factor influencing DFS in multivariate analysis was PBLVI by tumour cells; PBLVI-positive patients had a significantly higher likelihood ratio (P = 0.000001) of developing metastasis than their PBLVI-negative counterparts. This study documents the prognostic implication of PBLVI by tumour cells in T4 NSCLC.