Fluorescence in situ hybridization (FISH) has been developed as a powerful technology which allows direct visualisation or localisation of genomic alterations. The technique has been adopted to a range of applications in both medicine, especially in the areas of diagnostic cytogenetics, and biology. Topics described in this manual include: FISH on native human tissues, such as blood, bone marrow, epithelial cells, hair root cells, amniotic fluid cells, human sperm cells; FISH on archival human tissues, such as formalin fixed and paraffin embedded tissue sections, cryofixed tissue; simultaneous detection of apoptosis and xpression of apoptosis-related genes; comparative genomic ybridization; and special FISH techniques.