Abstract: 6β-AN(6β-acetoxy nortropane),a novel selective M₂-receptor agonist,causeddecrease in FR,TV,MVV and pO₂ and increase of pCO₂ when intravenous injection of 10 ug·kg^-1in conscious rabbits or 2,5, 20 ug·kg^-1 in conscious dogs was given(P<0.05 or 0.01).Theinhibitory effect on MVV exhibited a dose-dependent relationship.Small doses of 6β-AN icv(0.5,1,2,4 ug·kg^-1 in the conscious rabbits)and iva(6.25,0.5 and 1.0 ug·kg^-1 in anesthetized dogs)decreased FR,TV,MVV and pO2 and increased pCO₂ as well.These results were reversed after admi-nistration of AF-DX116 and enhanced after administration of pirenzepine.Thus,it appears that theinhibitory action of 6β-AN on respiration might be related to stimulation of the inhibitory M₂ cholinergic receptor in respiratory center.