Plant materials, containing14C-labeled lignins, were harvested at intervals up to 1 year after labeling. They were oxidized with sodium chlorite (NaC102) and nitrobenzene. Age of lignin appears to limit the degree of solubilization of lignin by NaC102. Nitrobenzene oxidation solubilized all lignins in wheat, oak, and kenaf but not all lignin in some pine samples. Klason and UV analysis of lignin content were compared with14C-content to determine percent lignin soluble in 3% sulfuric acid (Klason analysis solvent), corrected lignin contents, and UV absorptivity of lignin. Ten to 20% of most lignins were soluble in 3% sulfuric acid. When corrected Klason lignin contents were used, UV absorptivities at 280 nm were about 38 g−11 cm−1for wheat straw and kenaf lignins and 11 g−11 cm−1for pine lignin.