In this study we examined loss of heterozygosity (LOH) on chromosome 13q12-13 in 50 tumors from BRCA2 carriers in five families showing strong evidence of linkage to BRCA2. In addition to high frequency of LOH in female breast cancer, LOH was observed in tumors of the prostate, ovary, cervix, colon, male breast, and ureter. All detected losses involved the wild-type chromosome. These results suggest that BRCA2 is a tumor suppressor gene and may be involved in the tumorigenesis of several cancer types in addition to breast cancer.