Abstract This report describes the characterisation of cloned rat and human bradykinin B 1 receptors in African green monkey kidney fibroblast (Cos-7) cells. A ligand binding assay with [ 3 H ]des-Arg 10-kallidin was used to compare their pharmacology with respect to known bradykinin B 1 and B 2 receptor ligands. In addition, the pharmacology of T-kinin and its' derivative des-Arg 11-T-kinin was investigated. The cloned rat receptor had a similar pharmacology to that of the recently described mouse receptor and differs from that described for the human receptor. The rat receptor had a higher affinity for des-Arg 11-T-kinin than the human receptor. These differences in pharmacological properties may relate to the presence of T-kinin, bradykinin and their des-Arg derivatives as the major physiological peptides in rat and the predominance of kallidin and its derivatives in human. We confirm that the rat bradykinin B 1 receptor gene is organised in a two exon structure and differs from the human gene which has a three exon structure and we further examine the inducible expression of this gene in a wide range of tissues using Northern blotting.