1. The rapid progression of the collaborative sequencing programmes that are unravelling the complete genome sequences of many organisms are opening pathways for new approaches to gene analysis. As the sequence data become available, the bottleneck in biological research will shift to understanding the role of each of these genes. Techniques that enable the analysis of large sets of genes in one experiment will elucidate the interactions of genes in diverse biological systems. 2. Microarrays, which consist of large numbers of cDNA or oligonucleotides spotted onto a glass microscope slide, are one such technology. RNA isolated from two populations of cells, one control and one altered by experimental treatment or disease, is labelled with two different fluorochromes before being hybridized to the microarray. After a standard hybridization reaction, a scanner records the intensity of the two fluorochromes. The data can be analysed using special software that enables clustering of genes that have similar expression patterns. 3. Such powerful analysis techniques will provide information about genes whose functions are currently unknown and enhance our understanding of how genes interact to provide molecular control. This increase in knowledge about gene function will allow new targeted approaches for the development of drugs and/or gene therapies.