© 2003 by CRC Press LLC. Biochips and microarrays are technologies that will benefit directly from the research advances of the postsequencing era in genomics. Experimental genomics, in combination with the growing body of sequence information, promises to revolutionize the way cells and cellular processes are studied and diseases diagnosed and treated. Information on genomic sequence can be used experimentally with highdensity DNA arrays that allow complex mixtures of RNA and DNA to be interrogated in a parallel and quantitative fashion. DNA arrays can be used for many different purposes, especially to measure levels of gene expression (messenger RNA abundance) for tens of thousands of genes simultaneously. On the other hand, portable, self-contained biochips with integrated detection microchip systems have great potential for use by the physician at the point of care.