Lignin is a major component of the secondary cell wall. This complex phenolic polymer is derived mainly from three hydroxycinnamyl alcohol monomers named monolignols. After transport of the monolignols to the cell wall, lignin is formed through an enzymatically-initiated oxidative polymerization of these precursors. Whereas many studies have established that this polymerization involves peroxidases, the involvement of laccases is more speculative. The identification of the peroxidases and laccases specifically involved in lignification is complicated by the fact that these enzymes belong to multigene families. For instance, in Arabidopsis, there are 73 peroxidase and 17 laccase genes. In order to determine which peroxidases and/or laccases could be involved in the polymerisation of monolignols, several strategies have been considered: • Expression profiling in the highly lignified infloresecence stem by RT-PCR and promoter/GUS fusions • Presence in the cell wall proteome of stems • Characterization of homozygous knock-out Arabidopsis TDNA mutants and determination of the impact of the mutation on lignin content and composition. The results of this study will be presented and new information on the importance of several genes in lignification will be provided. Orthologs of poplar have been identified and are currently under study.