The new techniques of molecular cytogenetics, mainly fluorescence in situ hybridization (FISH) of DNA probes to metaphase chromosomes or interphase nuclei, have been developed in the past two decades. Many FISH techniques have been implemented for diagnostic services, whereas some others are mainly used for investigational purposes. Several hundreds of FISH probes and hybridization kits are now commercially available, and the list is growing rapidly. FISH has been widely used as a powerful diagnostic tool in many areas of medicine including pediatrics, medical genetics, maternal¿fetal medicine, reproductive medicine, pathology, hematology, and oncology. Frequently, a physician may be puzzled by the variety of FISH techniques and wonder what test to order. It is not uncommon that a sample is referred to a laboratory for FISH without indicating a specific test. On the other hand, a cytogeneticist or a technologist in a laboratory needs, from case to case, to determine which procedure to perform and which probe to use for an informative result. To obtain the best results, one must use the right DNA probes and have reliable protocols and measures of quality assurance in place. Also, one must have sufficient knowledge in both traditional and molecular cytogenetics, as well as the particular areas of medicine for which the test is used in order to appropriately interpret the FISH results, and to correlate them with clinical diagnosis, treatment, and prognosis.

Basic Concepts and Techniques.- Molecular Cytogenetics in Medicine.- Labeling Fluorescence In Situ Hybridization Probes for Genomic Targets.- Labeling Fluorescence In Situ Hybridization Probes for RNA Targets.- Basic FISH Techniques and Troubleshooting.- Evolving Techniques and Applications.- Chromosome Microdissection.- Primed In Situ Labeling.- Spectral Karyotyping.- Multicolor FISH.- Characterization of Constitutional Chromosome Abnormalities by Comparative Genomic Hybridization.- Color Banding.- Multicolor Fiber FISH.- Multi-Telomere FISH.- Fluorescence Genotyping for Screening Cryptic Telomeric Rearrangements.- Microarray CGH.- Special Applications in Chromosomal Disorders.- Molecular Approaches for Delineating Marker Chromosomes.- Interphase FISH for Prenatal Diagnosis of Common Aneuploidies.- Prenatal Diagnosis of Chromosomal Abnormalities Using Maternal Blood.- Preimplantation FISH Diagnosis of Aneuploidies.- Microdeletion Syndromes.- Molecular Detection of Uniparental Disomy.- Molecular Cytogenetics in Reproductive Pathology.- Special Applications in Oncology.- Interphase FISH Studies of Chronic Myeloid Leukemia.- Chromogenic In Situ Hybridization and FISH in Pathology.- FISH Detection of HER2 Amplification in Breast Cancer.- Comparative Genomic Hybridization in Cancer Investigations.- Simultaneous Fluorescence Immunophenotyping and FISH on Tumor Cells.- BAC Resource for Molecular Cytogenetics.