It is expected that by the year 2003 the entire human genome will be sequenced, providing us with new insight into human disease. The amount of human sequence information that is already available (only a few percent of the total) is, however, already much greater than can be routinely evaluated with existing, commonly used diagnostic technology. New technology based on attaching DNA to a chip for parallel hybridization analysis is generating much interest in both the basic research and the clinical diagnostic community. It will increase, by orders of magnitude, our ability to evaluate an individual's genetic heritage and to conduct basic genetic research. The new technology will be a major advance in screening for genetic diseases, but the ability to treat these newly understood genetic defects will lag significantly behind the new-found diagnostic capabilities.