It has been suggested that loss of the short arm of chromosome 3 is one of the most frequent abnormalities in human head and neck cancers including oral squamous cell carcinomas (SCC) and that one or more putative tumor suppressor gene(s) which may contribute to the initiation and/or progression of these tumors might be located on chromosome 3p. In this study, we examined the effects of introducing human chromosome 3 or 7 by microcell hybridization on the tumor-associated phenotypes of three different human oral SCC cell lines, HSC-2, HSC-3 and HSC-4. Transfer of a single chromosome 3p completely suppressed the tumorigenicity of all three parental cell lines, which showed a significant decrease in growth rate in vitro and morphological changes. In contrast, transfer of chromosome 7 had no effect on HSC-2 and HSC-4 cells, although it suppressed the tumorigenicity of HSC-3 cells without modifying their in vitro growth properties. Our findings provide additional confirmatory evidence that loss or inactivation of putative tumor suppressor gene(s) present on chromosome 3p might be primarily involved in the development of human oral SCC. The possibility that chromosome 7 may carry another tumor suppressor gene(s) is also discussed.