The following compounds have been prepared labeled with C14: cyanamide, urea, thiourea, dicyandiamide, and guanidine nitrate. Cyanamide was synthesized by heating radioactive barium carbonate at 850 °C. in a stream of ammonia and extracting with water the barium cyanamide so formed. Urea and thiourea were prepared from cyanamide by hydrolysis under suitable conditions. When an aqueous solution of cyanamide was heated, its dimer, dicyandiamide, was obtained and the latter compound was converted to guanidine nitrate by fusing with ammonium nitrate at 175° to 185 °C. The preparations of the above materials were carried out on a 5 to 10 millimole scale, and good yields were obtained in each case.