Lignifying xylem from tobacco (Nicotiana tabacum) expresses oxidase activity capable of oxidizing a range of chromogenic substrates by a non-peroxidative mechanism. These oxidases appear to be ionically bound to the cell wall and can be extracted using 1M NaCl. The extracted oxidases can oxidize the monolignol coniferyl alcohol. Extracts from xylem cell walls contain a number of different oxidase isoforms with isoelectric points in the neutral to mildly acidic range. Xylem from younger, apical tobacco stems yield a different set of oxidase isoforms than xylem from older, basal areas which suggests that oxidase isoforms may be differently expressed during xylem maturation. Non-denaturing SDS-PAGE confirms the presence of a band of oxidase activity (M r ca 100 kDa) in these extracts that has properties similar to those of the laccase-type polyphenol oxidases (p-diphenol: O 2 oxidoreductase; EC 1.14.18.1) previously identified in the lignifying tissues of trees. Ion-exchange chromatography on DEAE-Sepharose retained this 100 kDa laccase-like activity and resulted in a ten-fold purification and a six-fold increase in the recovery of oxidase activity, probably as the result of the removal of inhibitors. In contrast, a subsequent hydrophobic interaction chromatography step was unsuccessful, probably as a result of the precipitation of the laccase-like oxidase in the concentrated ammonium sulphate buffers required for this procedure.