In the past decade, microarray technology has become a major tool for high-throughput comprehensive analysis of gene expression, genotyping and resequencing applications. Currently, the most widely employed application of high-density oligonucleotide arrays (HDOAs) involves monitoring changes in gene expression. This application has been carried out in a variety of organisms ranging from Escherichia coli to humans. The recent near completion of the human and mouse genome sequences, however, as well as the genomes of other model experimental species, has allowed for novel applications of HDOAs, such as: the discovery of novel transcripts, mapping functionally important genomic regions and identifying functional domains in RNA molecules. Integrating all this information will provide novel global views of the locations of RNA transcription, DNA replication and the protein nucleic acid interactions that regulate these processes.