Advances in microarray technology enable massive parallel mining of biological data, with biological chips providing hybridization-based expression monitoring, polymorphism detection and genotyping on a genomic scale. Microarrays containing sequences representative of all human genes may soon permit the expression analysis of the entire human genome in a single reaction. These 'genome chips' will provide unprecedented access to key areas of human health, including disease prognosis and diagnosis, drug discovery, toxicology, aging, and mental illness. Microarray technology is rapidly becoming a central platform for functional genomics.