The BCR gene on chromosome 22 has received increasing attention because of its involvement in the Philadelphia (Ph′) translocation. For most restriction enzymes, this locus has been found to be nonpolymorphic. Two alleles have only been found when Taql-digested DNA is hybridized to a 5′ bcr-specific probe. We describe another two-allele polymorphism detected by the same probe in PvuII-digested DNA. The polymorphism is characterized by an additional PvuII site in the bcr region: this causes the appearance of an additional band of about 2.3 kb or 2.5 kb besides a 4.8-kb fragment in hybridizations with the 5′ bcr or a 3′ bcr probe. The incidence of the second allele is very low. It has only been found in some patients with hematopoietic malignancies and in a group of volunteers having a leukemia patient in their families.