The B2 bradykinin receptor (B2BKR) mediates most of the inflammatory actions of bradykinin. To evaluate its potential role in allergic diseases, we assessed the structure of the human B2BKR gene. Screening a human placenta genomic DNA library identified only clones containing exons 2 and 3. Human placenta and colon tissues were used for 5' rapid amplification of complementary DNA ends to identify nine exon 1 clones, each containing one 9 bp and two 1 bp deletions compared with published sequences. Exon 1 genomic polymerase chain reaction of human leukocyte DNA revealed two distinct products, which were shown to differ by the presence or absence of the 9 bp deletion. Alleles with the 9 bp deletion were designated as (-)^21-29, whereas alleles without the deletion were designated as (+)^21-29. Genomic polymerase chain reaction in 39 Caucasian, 31 African-American, and 32 Asian normal subjects revealed a highly significant difference in the allelic frequency of the two genotypes, primarily because of an absence of the (+)^21-29 allele in Asian subjects. Analysis of steady-state B2BKR messenger RNA levels by reverse-transcription polymerase chain reaction in heterozygous normal subjects revealed consistently higher expression of (-)^21-29 transcripts. To investigate the potential clinical significance of the exon 1 polymorphism, 21 patients with angioedema and C1 inhibitor deficiency were genotyped. None were homozygous for the (+)^21-29 allele (p = 0.0088 compared with normal subjects). In contrast, two patients with immunochemical evidence of hereditary angioedema without history of clinical angioedema were (+)^21-29 homozygous. These results suggest that the B2BKR genotype may influence clinical status in diseases characterized by involvement of bradykinin. (J Allergy Clin Immunol 1997;99:134-46.)