A molecular clone encoding a beta3-adrenoceptor was isolated from a canine genomic library. The cloned receptor exhibited a pharmacological profile similar to that of other species: in particular, high efficiency of the two selective beta3-adrenoceptor agonists, CL 316,243 (disodium(R,R)-5[2[[2-(chlorophenyl)-2hydroxyethyl]-amino]propyl]- 1,3-benzodioxole-2,2-dicarboxylate) and ICI 201651 ((R)4-(2-hydroxy-3-phenoxypropylaminoethoxy)-N-(2-methoxyethyl)phe noxy acetic acid) and a low affinity for the radioligand (-)-[3-(125)I]-iodocyanopindolol. Interestingly, CGP 12177A ((+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one), which is described as a partial agonist for the human receptor, was a full agonist for the canine receptor. After expression and stimulation of the canine beta3-adrenoceptor in stably transfected Chinese hamster ovary cells there was a very low accumulation of cAMP, suggesting weak coupling to Gs-protein and adenylyl cyclase. However, the response was much better in human embryonal kidney cells transfected with the canine beta3-adrenoceptor gene. The cloning of the canine beta3-adrenoceptor and the insights gained from its pharmacological characterization may allow the development of selective compounds for use in the treatment of obese dogs.