To identify genes involved in the response to the fire blight pathogen Erwinia amylovora in apple (Malus×domestica), expression profiles were investigated using an apple oligo (70-mer) array representing 40, 000 genes. Blossoms of a fire blight-susceptible apple cultivar Gala were collected from trees growing in the orchard, placed on a tray in the laboratory, and spray-inoculated with a suspension of E. amylovora at a concentration of 10(8) cfu ml(-1). Uninoculated detached flowers served as controls at each time point. Expression profiles were captured at three different time points post-inoculation at 2, 8, and 24 h, together with those at 0 h (uninoculated). A total of about 3500 genes were found to be significantly modulated in response to at least one of the three time points. Among those, a total of 770, 855, and 1002 genes were up-regulated, by 2-fold, at 2, 8, and 24 h following inoculation, respectively; while, 748, 1024, and 1455 genes were down-regulated, by 2-fold, at 2, 8, and 24 h following inoculation, respectively. Over the three time points post-inoculation, 365 genes were commonly up-regulated and 374 genes were commonly down-regulated. Both sets of genes were classified based on their functional categories. The majority of up-regulated genes were involved in metabolism, signal transduction, signalling, transport, and stress response. A number of transcripts encoding proteins/enzymes known to be up-regulated under particular biotic and abiotic stress were also up-regulated following E. amylovora treatment. Those up- or down-regulated genes encode transcription factors, signaling components, defense-related, transporter, and metabolism, all of which have been associated with disease responses in Arabidopsis and rice, suggesting similar response pathways are involved in apple blossoms.