Background Formamides are common motifs of biologically-active compounds (e.g. formylated peptides) and are frequently employed as intermediates to yield a number of other functional groups. A rapid, simple and reliable route to carbonyl - 11 Cformamides would enable access to this important class of compounds as in vivo PET imaging agents. Results A novel radiolabelling strategy for the synthesis of carbon-11 radiolabelled formamides ( 11 Cformamides) is presented. The reaction proceeded with the conversion of a primary amine to the corresponding 11 Cisocyanate using cyclotron-produced 11 CCO 2 , a phosphazene base (2- tert -butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine, BEMP) and phosphoryl chloride (POCl 3 ). The 11 Cisocyanate was subsequently reduced to 11 Cformamide using sodium borohydride (NaBH 4 ). 11 CBenzyl formamide was obtained with a radiochemical yield (RCY) of 80% in 15 min from end of cyclotron target bombardment and with an activity yield of 12%. This novel method was applied to the radiolabeling of aromatic and aliphatic formamides and the chemotactic amino acid 11 Cformyl methionine (RCY = 48%). Conclusions This study demonstrates the feasibility of 11 C-formylation of primary amines with the primary synthon 11 CCO 2 . The reactivity is proportional to the nucleophilicity of the precursor amine. This novel method can be used for the production of biomolecules containing a radiolabelled formyl group.