This investigation of oral squamous carcinoma in five individuals revealed that four of the patients were constitutionally heterozygous at the c-Ha-ras-1 locus and that the tumour from one patient had lost that heterozygosity. The loss of c-Ha-ras-1 alleles provides a useful marker for detecting deletions of genetic material located on the short arm of chromosome 11 (11p) and has been found in association with a number of malignant tumours but has not been previously described in carcinoma of the head and neck. The repeated association of 11p deletions with malignancies has led to the postulation of a recessive cancer gene or tumour suppressor gene at this location involved in carcinogenesis and tumour progression. This study indicates that such a mechanism may contribute to the development of oral squamous carcinoma.