A chemical degradation scheme is reported, which permits the measurement of the radioactivity of each carbon atom of nicotinic acid. Nicotinic acid is decarboxylated by heating with copper chromite to give carbon dioxide (C-7) and pyridine. The pyridine is converted into 4-nitropyridine 1-oxide, which is heated with aqueous calcium hypobromite to give tribromonitromethane. Combustion of the latter gives carbon dioxide derived from C-4 of the nicotinic acid. Nicotinic acid is also reduced to nipecotic acid, which is oxidized to succinic acid by acidic potassium permanganate. Stepwise degradation of the succinic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-3, C-6 and C-4, C-5 of the nicotinic acid. Benzoylation of the nipecotic acid, followed by oxidation with permanganate at pH7, gives 5-amino-4-carboxyvaleric acid; this is converted into 2-methyleneglutaric acid by the action of nitrous acid. Hydrogenation of the 2-methyleneglutaric acid over rhodium in methanol gives 2-methylglutaric acid, which is oxidized with dilute chromic acid to acetic acid. Stepwise degradation of the acetic acid by standard procedures gives two samples of carbon dioxide, which correspond to C-2 and C-3 of the nicotinic acid. Thus the radioactivities of C-2, C-3, C-4 and C-7 are determined directly and those of C-5 and C-6 by difference. The method was shown to be isotopically valid for [2,3,7-(14)C]-, [4,6-(14)C(2)]- and [5-(14)C]-nicotinic acid.