3-[3-(Piperidinomethyl) phenoxy] alkyl, N-cyano-N′-[ω-[3-(1-piperidinylmethyl) phenoxy] alkyl] guanidine and 2-(5-methyl-4-imidazolyl) methyl thioethyl derivatives containing fluorescent functionalities were synthesized and the histamine H2 receptor affinity was evaluated using the H2 antagonist [125I]-aminopotentidine. The compounds exhibited weak to potent H2 receptor affinity with pKi values ranging from< 4 to 8.85. The highest H2 ...