The radiosynthesis of imidazole ring labeled [14c]metiamide, [1k]cimetidine and ["k]impromidine are described involving the reaction of the key common intexmediate 2-dimethyldithiocyanoiminocarbonate/methylamine and the novel dihydroknidazdiazepine 0, res ectively. The ring labeled precursor @ was prepared in five steps from potassium mCi/mmol. [ 1 B Clcyanide in an overall radiochemical yield of 63%, and having a specific activity of 9.3 14C]imidazol-5-yl)-methyl]thio]ethanamine. histamine H2-receptor antagonist, histamine H2receptor agonist, [14C]imidazole ring labeled.