A series of (2-aryl-5-methylimidazol-4-ylcarbonyl) guanidines and (2-aryl-5-methyloxazol-4- ylcarbonyl) guanidines were synthesized and evaluated as NHE-1 inhibitors. The structure– activity relationships well matched those of furan derivatives, which were previously investigated. The (2, 5-disubstituted) phenyl compounds showed better activities than the other analogues in both imidazole and oxazole compounds. Especially, 2-(2, 5- ...