The stereochemistry of interaction of several 1,3-oxathiolane muscarinic ligands is considered and discussed. On the basis of the identical absolute configuration of the most affinitive enantiomers of agonists and antagonists it is suggested that the two kinds of ligands interact with an identical binding site, namely the recognition site of Acetylcholine. The hypothesis is extended to other muscarinic antagonists like the bulky esters of choline, 2,2-disubstituted-1,3-dioxolanes and Atropine-like compounds; a model for such an interaction is proposed.