Fluorescence in situ hybridization (FISH) or molecular cytogenetics is curr
ently recognized as a reliable, sensitive, and reproducible technique for i
dentifying the copy number and structure of chromosomes. FISH combines mole
cular genetics with classic cytogenetics and allows simultaneous morphologi
c evaluation on a single slide. Centromeric DNA probes are used to detect s
pecific chromosomes and telomeric probes to demonstrate all chromosomes, Se
quence-specific probes can localize in situ a single gene copy on a specifi
c chromosome locus, FISH allows cytogenetic investigation of metaphase spre
ads and interphase nuclei. Several protocols have been proposed to analyze
preparations from fresh samples or archival material. Comparative genomic h
ybridization (CGH) is a novel cytogenetic technique, which combines FISH wi
th automatic digital image analysis. Comparative analysis of the hybridizat
ion products of tumor DNA and reference DNA with normal metaphase chromosom
es, each labeled with color different fluorochrome, can retrieve chromosoma
l imbalances of the entire genome in a single experiment. FISH and CGH are
powerful morphologic tools in understanding physiologic mechanisms and in r
esolving problems of the pathogenesis of several diseases, These techniques
shed light on the cytogenetic background in many endocrinological disorder
s, providing a better understanding of the activities and alterations of en
docrine cell function.