The microarray technology is a very powerful technology that combines molecular biology and computer technology to analyze the gene expression levels for most or all of the genes in a whole genome simultaneously, at very high resolutions. This technology has wide applications, including gene interaction studies for discovery of genes responsible for different diseases; classification of cancers and other diseases; prediction of clinical outcomes or prognosis for different diseases; response to therapy and development of new therapeutic agents, including gene therapy. It is therefore a very potent, unbiased and sensitive technology for the discovery of novel genes involved in the pathogenesis or control of diseases including cancers and autoimmune diseases. In the present study, we seek to give a clear and detailed account of the microarray gene expression protocol using the mouse T-cell gene expression profile, including challenges involved and how to overcome them, as well as detailed analysis of results obtained.