SUMMARY p53 and p21WAF-1 expression were examined by immunohistochemistry in neoplastic, preneoplastic and normal bronchial mucosa in 60 patients with lung cancer in order to investigate the role of the corresponding genes in lung carcinogenesis. p53 expression was present in 43% of the tumours, 27.5% of the preneoplastic lesions and in normal mucosa, in 16.7% of the patients. p21WAF-1 expression was present in 60% of the tumours, 47.5% of the preneoplastic lesions and in normal rnucosa, in 63% of the patients. There was a statistical significant trend of p53 - positive tumours to coexist with p53 - positive preneoplastic lesions in the same patient, and patients with p53 - positive tumors or preneoplastic lesions to exhibit also p53 expression in normal mucosa. There was a statistical significant trend of p21WAF-1 positive tumours to coexist with p21WAF-1 positive preneoplastic lesions in the same patient. These results may indicate that abnormalities in p53 and WAF-1 genes are early events in lung carcinogenesis and that p53 expression in non-neoplastic mucosa is an indicator of lung field cancerization and may uncover increased risk of non-neoplastic mucosa to progress into cancer. Pneumon 1999, 12 (2): 93-103