Technical Abstract: Eutypa lata is a vascular pathogen of woody plants. In the present study we (i) determined which component(s) of the cell wall polymers were degraded in naturally infected grapevines and in artificially inoculated grape wood blocks; (ii) compared the pattern of wood decay in the tolerant grape cultivar Merlot vs. the susceptible cultivar Cabernet Sauvignon; and (iii) identified secondary metabolites and hydrolytic enzymes expressed by E. lata during wood degradation. Biochemical analyses and cytochemical study indicated that glucose-rich polymers were primary targets of E. lata. Structural glucose and the hemicellulose fraction of the plant cell wall as well as starch were depleted in infected woods identically in both cultivars. Moreover, the more tolerant cultivar Merlot always had more lignin in the wood than the susceptible cultivar Cabernet Sauvignon, indicating that this polymer may play a role in disease resistance. In vitro assays demonstrated the production by E. lata of oxidases, glycosidases and starch degrading enzymes. Phytotoxic secondary metabolites were also produced but our data suggest that they may bind to the wood. Finally, we demonstrated that free glucose in liquid cultures repressed primary but not secondary metabolism.