N-Alkyl-N'-cyano-N"-(substituted phenyl-pyridinylmethyl) guanidine derivatives were synthesized and tested for inhibitory activity against gastric secretion in rats. Several of the compounds synthesized showed an inhibiting activity as potent as that of cimetidine against basal gastric secretion but showed less potent activity than cimetidine against histamine-stimulated gastric secretion. Some structure-activity relationships are discussed.