A proportion of human breast cancers result from an inherited predisposition to the disease. Mutations in the BRCA2 gene confer a high risk of breast cancer and are responsible for almost half of these cases. The recent cloning of the human BRCA2 gene has revealed that it encodes a large protein having little significant homology to known proteins. Here we describe the mouse Brca2 gene. The gene maps to mouse chromosome 5, consistent with its location on human chromosome 13q12. We have sequenced cDNA for the entire 3329 amino acid Brca2 protein and this has revealed that, like Brca1, Brca2 is relatively poorly conserved between humans and mice. Brca2 is transcribed in a diverse range of mouse tissues, and the pattern of expression is strikingly similar to that of Brca1. Taken together, our data highlight some intriguing similarities between two genes involved in inherited breast cancer susceptibility.