The replacement of the imidazole ring of cimetidine with a bicyclic system (imidazo[1,2-a]pyridine), reported in the literature, produced compounds endowed with potent antiulcer activity. In this paper we describe the synthesis of imidazo [2,1-b]thiazoles and thiazolines bearing the side chain of metiamide, cimetidine and ranitidine: the compounds obtained, tested on gastric lesions induced in rats by ethanol and by stress, were devoid of antiulcer activity.