The effect of Phaeomoniella chlamydospora infection was evaluated in three grapevine cultivars, in relation to the variation in phenolic compounds within the host. Young plants of Vitis vinifera (cv. Chardonnay, Touriga Nacional and two clones of cv. Aragonez) were infected using two strains of Pa. chlamydospora and were harvested after five months from inoculation. Overall, a localised increment in the amount of total phenolics within a methanolic extract of grapevine wood tissue was observed following infection. Such pattern was also manifested by a localised increase in non-tannin phenolics. HPLC analysis was used to identify the host phenolic compounds, which were mostly affected by the host-pathogen interaction. trans-Resveratrol was found to augment very significantly in both cv. Chardonnay and cv. Touriga Nacional following infection. -Viniferin also increased considerably in infected plants of cv. Touriga Nacional. Significant differences were encountered among infected plants depending not only on the cultivar, but also on the site of inoculation. Overall, cv. Chardonnay and cv. Touriga Nacional contained a higher amount of infection-induced phenolic compounds than both cv. Aragonez clones. Infection of young shoots also led to a greater accumulation of phenolic compounds than that of the trunk. Results are discussed in view of understanding the role of phenolic compounds and especially trans-resveratrol in grapevine defences against Pa. chlamydospora.