The wide availability and use of DNA microarrays has brought the power of whole-genome functional characterization to a large variety of research environments. Microarrays, however, also introduce significant infrastructural and analytical concerns with respect to the long-term warehousing, annotation, and visualization of immense data sets. The Longhorn Array Database (LAD) is a MIAME-compliant microarray database that operates on PostgreSQL and Linux. It is a free and completely open-source software solution, and provides a systematic and proven environment in which vast experiment sets can be safely archived, securely accessed, biologically annotated, quantitatively analyzed, and visually explored. This unit provides the complete set of information needed to successfully deploy, configure, and use LAD for the purposes of two-color DNA microarray analysis and visualization.