FISH is a new technique which is used to localize a specific sequence on chromosome,It has been widely used in the research of human genome project.With FISH,a SCP,a cosmid or a YAC can be localized on the metaphase chromosome,and a chimeric YAC can also be identified.Gene mapping can be done at the resolution of 50 kb with FISH on the interphase nuclei.Now FISH of a gene on the strechted chromatic fibre can be done,the length of the gene can directly be measured and the gene can be localized at high resolution. In a word. FISH is playing a more and more important part in the human genome research.