The four isomers of 2-cyclohexyl-2-phenyl-5-[(dimethylamino)methyl] -1,3-oxathiolane methiodide were prepared. Their absolute configuration was attributed by means of X-ray crystallography and circular dichroism. The compounds were tested on rat bladder and guinea pig ileum and heart, and their antimuscarinic potency was evaluated and expressed as pA2. The results show that the introduction of a chiral center into position 2 brings about a small but definite enantioselectivity on rat bladder and guinea pig ileum which is not seen for guinea pig heart. This supports the view that differences exist among the muscarinic receptors of these tissues (M2 receptors). Comparison of the absolute configuration of the antagonists studied in this and in the preceding paper2 and that of strictly related agonists supports the hypothesis of a common binding site for agonists and antagonists of this kind.