The proto-oncogene c-myc encodes a highly conserved nuclear phosphoprotein that functions as a transcription factor in the cell. The discovery of deregulated c-myc in a variety of tumours and the ability of c-myc to transform cells either alone or in cooperation with the ras oncogene indicate that the activation of c-myc is involved in tumorigenesis. In addition to its tumorigenic ability, c-myc has also been implicated in apoptosis and the control of normal cell growth. The identification and characterization of the target genes of c-myc may help us to decipher the mechanism by which c-myc functions in various biological processes. To identify the genes regulated by c-myc, we compared the gene expression profiles between c-myc wild-type and c-myc mutant rat fibroblast cells using the cDNA glass microarray method. After rat EST clones were sequence verified and annotated, we assembled unique 4,400-element cDNA microarrays on glass slides. Using these microarrays, we studied differential gene expressions between wild-type c-myc and c-myc−/− rat fibroblast cells under different conditions. We confirmed the differential expression of some candidate genes by northern blot. We hope that these microarray studies may elucidate the pathways that are regulated by c-myc, which may in turn help us to understand the mechanism by which c-myc functions in normal, neoplastic or apoptotic cells.