In order to corroborate the assumption that a candidate tumor suppressor gene is located on chromosome 13q21-22 between D13S1313 and D13S162, we examined loss of heterozygosity of six microsatellite markers in this region in 98 sporadic breast tumors. Our data demonstrate that loss of heterozygosity at 13q21-22 is not solely caused by genetic changes in BRCA2, but is also attributable to another gene in this region. There is strong indication of a new tumor suppressor gene located between D13S1313 and D13S162, most probably adjacent to D13S1308, which could play a role in sporadic breast cancer.