The actions of bradykinin (BK) in mammals are mediated through the activation of the B1 and B2 BK receptors. The only BK receptor that has been cloned from a non-mammalian species is a B2-like receptor from the chicken (termed the ornithokinin receptor). Pharmacological studies have demonstrated the presence of BK receptors in tissues of teleost fishes , such as trout and cod, but the ligand-binding properties of these receptors differ appreciably from those of the mammalian and chicken receptors. We report here the cloning of a B2-like receptor in zebrafish that shares 35% identity with human B2 and 30% identity with human B1. Phylogenetic analyses confirm a closer relationship with B2 than B1. The receptor gene was mapped to linkage group 17, which is syntenic to the human B2-B1 gene region. After functional expression of the zebrafish B2 receptor in mammalian cells, nanomolar concentrations of trout BK ([Arg (0),Trp(5),Leu(8)]-BK) and the derivative [des-Arg(0),Trp(5),Leu(8)]-BK (where 'des' indicates a missing amino acid) induced a significant transient rise in intracellular free Ca(2+). The B1-selective analogue [ Arg(0),Trp(5),Leu(8),des-Arg(9)]-BK was inactive at nanomolar concentrations. Taken together, these results strongly support the gene' s identity as a piscine orthologue of the mammalian B2 receptor.