Stress triggers changes in gene expression mediating important adaptive and maladaptive responses. The full repertoire of genes whose expression in the adrenal medulla is altered by stress has not been previously determined. In this study, gene profiling (RAE 230 2.0 Affymetrix) was applied to elucidate global changes in gene expression in adrenal medulla of rats exposed to 2-h immobilization (IMO) stress once or repeatedly for 6 consecutive days. The number of transcripts significantly (P < 0.01) altered with single IMO (651 up, 487 down) was more than with repeated IMO (370 up, 195 down). The annotated transcripts were further analyzed and categorized. The largest numbers of changes were in mRNA levels in the transcription factor and cell signaling categories. Robust changes were also observed in transcripts related to growth factors, apoptosis, neurosecretion/neuropeptides, heat shock proteins, structural proteins, chemokines, cytokines, metabolism/lipid-metabolism, and proteases. Many (>80%) were uniquely induced by single IMO. About half of transcripts changed by repeated IMO were also responsive to single IMO. Pathway analysis was applied to identify direct interactions and common targets among gene products altered by single and repeated IMO. In this paper, we briefly describe the most pronounced changes observed, with emphasis on those that may provide new insight into the common and distinct mechanisms whereby the adrenal medulla responses to a first encounter with stress compared to repeated exposure to the same stressor.