The synthesis and pharmacological activity as muscarinic antagonists of a number of 2-alkylthio-2,2-diphenylacetic acid esters are reported. The compounds studied are potent muscarinic antagonists and many of them show from moderate to high selectivity toward M2 or toward M1 and M2 receptors when tested on tissues but lack selectivity on five muscarinic human receptors (m1-m5) cloned and expressed in CHO-K1 cells. As a consequence, the compounds behave as functionally selective antagonists. Those showing M2 selectivity appear to be good drug candidates for the treatment of cognitive disorders connected with central cholinergic deficit.