Nicotinic acid-6- 14C and nicotinamide adenine dinucleotide-carbonyl- 14C were rapidly metabolized in T. wilfordii Hook. with formation of all compounds in the pyridine nucleotide cycle. Nicotinic acid-6- 14C and the nicotinamide moiety of NAD were efficiently incorporated into wilfordic acid and hydroxywilfordic acid, the pyridinium moieties of the ester alkaloids. The structures of wilfordic acid and hydroxywilfordic acid were confirmed using GLC-MS. The molecular formulae of the four isolated alkaloids were determined by high resolution MS and agreed with earlier results based on elemental analysis.