Gene expression data from Arabidopsis thaliana microarray experiments are incorporated in PathoPlant. Normalized (print-tip-group lowess method) expression data from experiments with Arabidopsis thaliana upon pathogen infection or elicitor treatment are searchable. Two modes of search are available. A list of genes can be submitted to obtain expression data on these genes for all stimuli annotated in PathoPlant. This search can be restricted to certain induction factors. Alternatively, up to 3 different stimuli can be submitted for a search for genes regulated by these stimuli. Stimuli can be combined to find only genes that match all stimuli (AND operator) or for displaying all genes that match at least one of the stimuli (OR operator). This search can also be restricted to certain induction factors. Besides the induction factors given for a single experiment, mean induction factors were determined that cover results from replicate experiments. In order to validate mean and single induction factors, the number of replicates (n) and base-10 logarithm of standard deviation are given. The result list can be resorted by Locus, Description, Stimulus, Factor, and Mean factor by clicking on the respective column header. A list of genes obtained by a expression search can directly be submitted to the Search by locus/gene ID form in PathoPlant. Additionally, the gene list can be transferred to AthaMap for a transcription factor binding site analysis.