The aim of the present study was to evaluate the expression of blood group antigens in squamous bronchial metaplasia in order to determine whether this factor could identify patients at risk of lung cancer. In total, 100 bronchial biopsies were included in the present study. The cases were classified according to the World Health Organization grading system. Immunohistochemical stains for histo-blood groups A and B, and reactivity tests to p53 and the cellular proliferation index were performed. A total of 56 (56%) patients belonged to blood group A. Among them, six (10.7%) patients who did not express antigen in squamous metaplasia, showed carcinoma at the moment of the biopsy (n = 3) or developed synchronous lung carcinoma (n = 3). A total of nine (9%) patients belonged to blood group B. Loss of antigenic expression was observed in five cases. All of them developed synchronous lung carcinoma. The patients with low- and high-grade dysplasia developed lung cancer in 71 and 100% of the cases, respectively. In conclusion, the findings of the present study suggest that the loss of histo-blood antigens expression is an event in the carcinogenesis of bronchial mucosa and it is usually associated with high-grade lesions and hyperproliferative activity.