Two mammalian genes encoding bradykinin (BK) receptors termed B1and B2have been identified by molecular cloning techniques. Some pharmacological data suggest the existence of further subtypes of the B2receptor. To unambiguously determine whether additional genes encoding B2BK receptors might exist in mammals, steps have been taken toward the generation of mice with a "knockout" of the BK B2receptor. A genomic clone of the mouse B2BK receptor was isolated and its coding sequence determined by DNA sequence analysis. A physical map of the DNA flanking this coding sequence was generated. A vector, pBS-KO-1, was constructed for targeted disruption of the mouse B2receptor gene. This vector contains 1 kb (kilobase) of DNA upstream of the mouse B2receptor coding sequence, a neomycin resistance gene (neo), and 5.4 kb of DNA downstream of the B2receptor coding sequence. Thus, the correct homologous recombination event will result in a chromosome in which the coding sequence for the mouse B2BK receptor is replaced with the neomycin resistance gene. pBS-KO-1 was transfected into embryonic stem cells, and clones containing a targeted disruption of the mouse B2BK receptor were identified.Key words: bradykinin, G-protein-coupled receptor, embryonic stem cells, gene targeting, homologous recombination.