A series of novel compounds having a benzothiazoline skeleton was studied for their structure-activity relationship (SAR) with respect to Ca2+ antagonistic activity. As test compounds, analogues of 3-acyl-2-arylbenzothiazolines (3) were synthesized. Benzothiazoline derivatives (3) exerted higher Ca2+ antagonistic activity than the corresponding thiazolidine derivatives (2). Effects of substituents