We analyzed the loss of heterozygosity of the long arm of chromosome 4 in 40 oral cancers, using 16 microsatellite markers based on data from the human genome sequence, and defined the deletional mapping of the region with putative tumor suppressor genes. Our data revealed two distinct commonly deleted regions around the markers, D4S2623 and D4S1644, with an allelic deletion of 44 and 39%, respectively. Additional mapping and use of the markers near one of these hot spots narrowed down the minimally deleted region about 1.5 Mbp around the marker, D4S2623. Caspase 6 is localized 280 kb from the marker, D4S2623. Fine mapping of this region with possible tumor suppressor gene suggests caspase 6 as a putative tumor suppressor gene. Further molecular analysis of caspase 6 should be performed to clarify its role in oral carcinogenesis.