The aim of molecular diagnostics is preferentially to detect a developing disease before any symptoms appear. There has been a significant increase, fueled by technologies from the human genome project, in the availability of nucleic acid sequence information for all living organisms including bacteria and viruses. When combined with a different type of instrumentation applied, the resulting diagnostics is specific and sensitive. Nucleic acid-based medical diagnosis detects specific DNAs or RNAs from the infecting organism or virus and a specific gene or the expression of a gene associated with a disease. Nucleic acid approaches also stimulate a basic science by opening lines of inquiry that will lead to greater understanding of the molecules at the center of life. One can follow Richard Feynman's famous statement "What I cannot create, I do not understand."