Heal and neck squamous cell carcinomas show frequent cytogenetic alterations involving the long arm of chromosome 13. To define the extent of 13q deletions and to identify the minimal areas of chromosome loss, 48 primary squamous cell carcinomas of the head and neck were analyzed for loss of heterozygosity using 11 different polymorphic loci. About 67% of the tumors displayed loss of genetic material at 13q. Most of the cases showed loss of the entire long arm of the chromosome. However, the presence of partial deletions in 10 cases provided evidence of the existence of two preferential sites of chromosome loss at 13q32-ter and 13q14.2-q14.3. The colocalization of the 13q14 minimal region of deletion with the retinoblastoma (RB) gene, which has been proposed as an oncosuppressor in diverse tumor types, prompted us to verify the involvement of this gene in the development of head and neck cancer. No significant variation in RB protein or RB mRNA expression was detected, thus excluding a role for such a gene in the genesis of this type of tumor. Taken together, our data suggest the existence of two new tumor suppressor genes (one close to and one distal to RB), which play a role in the development and/or progression of head and neck squamous cell carcinomas.