BACKGROUND AND AIMS: The interaction between the gall-forming grapevine parasite, phylloxera, and the susceptible grapevine species Vitis vinifera was investigated. METHODS: Phylloxera and grapevines were cocultivated using both potted and micropropagated grapevines. Development of nodosities on primary roots was studied by microscopy and histochemistry, and nodosities were analysed for biochemical changes and changes in gene expression. KEY RESULTS: Within a nodosity, phylloxera fed at a site in the root cortex. Nodosity development was characterized by swelling of the root tissue distal to the feeding site, lack of development of a suberized endodermis, and starch and amino acid accumulation, and was eventually followed by root necrosis. No evidence of a defence response was observed in pre-necrotic nodosities, but defence-type responses were observed in tissue adjacent to necrotic regions. Changes in gene expression were not detected by northern hybridization using DNA probes encoding a range of V. vinifera transcripts. CONCLUSIONS: Nodosities on V. vinifera potentially function as nutrient reservoirs, and defence responses to phylloxera attack were not detected.