The relative lack of specifi city of atropine as a competitive antagonist of muscarinic receptors is a frequent cause of undesirable parasympathetic side effects. Consequently, new tropane alkaloids with potentially greater selectivity are usually seen with real interest. The cholinergic antagonistic effects of a purifi ed mixture of tropane alkaloids extracted from Schizanthus hookeri were evaluated in rat ileum. For this purpose, ileal segments were obtained from randomly selected male Sprague-Dawley rats, and the effect of 1 · 10 −4 , 1 · 10 −3 , and 1 · 10 −2 mg/mL of the purifi ed mixture of alkaloids on the contractile response of the ileum induced with increasing doses of carbachol (5 · 10 −8 − 8 · 10 −4 M) was determined. The results were compared with those obtained in the presence of 3.46 · 10 −7 , 3.46 · 10 −6 , and 3.46 · 10 −5 mg/mL atropine as an agonist. Tropane alkaloids extracted from Schizanthus hookeri competitively antagonized acetylcholine muscarinic receptors.