The basal cell nevus syndrome is an autosomal dominant disease, one of the most prominent phenotypic features of which Is a large number of cutaneous basal cell carcinomas. The gene whose mutation underlies this disease has been mapped to chromosome 9q22. 3-q31, and basal cell carcinomas frequently have allellc losses including this site. We report here that the chromosome 9q22. 3-q31 lost in 24 basal cell carcinomas from basal cell nevus syndrome patients was the one predicted by linkage to contain the wild-type gene. Hence these data are compatible with the expectation that the product of the basal cell nevus syndrome gene acts as a tumor suppressor.