Objectives: The aim of this work was to investigate the secretor status of patients with oral pre-cancerous and cancerous lesions and ABH antigens expression in fixed tissue sections of these patients. Study design: To reveal A, B and H antigens in tissue sections of patients with precancerous and cancerous oral lesions (n= 54) we used a modified specific red cell adherence technique (SRCA-test). Normal endothelial cells expressed ABH antigens, the presence of indicator erythrocytes at the lumen of the blood vessels served as a built in positive control. The test results were graded from negative adherence to very strongly positive adherence. Negative adherence was defined as a complete absence of adhered indicator erythrocytes. A strongly positive reaction was defined as a sheet of indicator erythrocytes adhered to the epithelia cells. Results: In 31 of the 54 samples analyzed the test showed slightly positive results on atypical areas, and there was a complete antigen deletion in areas histologically affected by neoplasia. Sixteen samples showed a total absence of ABH antigens in both histologically normal and pathological areas. As a working hypothesis, we propose that areas of SRCA-test negative epithelium are closely related to invasive carcinomas and may be their precursor lesions. Further it is suggested that areas of blood group isoantigen negative epithelium showing atypia, or in some instances near normal histology, may give rise to relatively low grade carcinomas. Conclusions: Considering these results we suggest the use of this method to monitor probable preneoplastic lesions in risk population, specially in those with no secretor status.