The pharmacological profile of NK2 binding sites has been characterised in homogenates of rabbit urinary bladder and compared with that present in homogenates of hamster bladder. In both species, [125I]neurokinin A-specific binding to urinary bladder membranes was displaced by neurokinin A and the NK2 agonist [beta-Ala8]neurokinin A-(4-10) whilst the NK1 ligands [Sar9,Met(O2)11]substance P and (+/-)-CP-96,345, and the NK3 agonist, senktide, were only weak displacers or ineffective. At rabbit NK2 sites, the rank order of affinity of NK2 receptor-selective antagonists was; MEN 10,376 > MEN 10,207 > L-659,877 >> R 396. In contrast, the rank order of displacement of [125I]neurokinin A-specific binding to hamster bladder membranes was: L-659,877 > R 396 > MEN 10,376 > MEN 10,207. These data demonstrate that [125I]neurokinin A binds to pharmacologically distinct NK2 binding sites in hamster and rabbit urinary bladder.