A series of N-sulfamoyl and N-sulfonyl amidines have been prepared and tested in vitro for Hz antihistamine activity on guinea pig atrium. In addition, several selected compounds were assessed as inhibitors of gastric acid secretion induced by histamine in anesthetized dogs. Structure-activity relationship studies showed that those compounds containing 2- [(diaminomethylene) amino] thiazole exhibited potent H2-receptor antagonist activity. ...