The synthesis and biological evaluation of a new class of histamine Hz antagonists with N- cyano-N'-[~-[3-(1-piperidinylmethyl) phenoxy] alkyl] guanidine partial structure are described as part of an extensive research program to fmd model compounds for the development of new radioligands with high Hz affinity and specific activity. High receptor affinity is achieved by an additional (substituted) aromatic ring, which is connected with the third guanidine N ...