Ammonium [14C]thiocyanate was prepared from potassium [14C]cyanide with a radiochemical yield of 90%. [14C]hydrocyanic acid, generated from potassium [14C]cyanide by sulphuric acid, reacts with aqueous ammonia and elemental sulphur in the presence of trace amounts of ammonium sulphide to yield ammonium [14C]thiocyanate.