The CytoGenomics Core provides an invaluable technical resource to the investigators of the BWH, MGH, and affiliated institutions. Services are also available to external academic and commercial laboratories; these should contact us via our website for sample submission and pricing. Cytogenetic studies can provide insight into regions of the genome that are pathogenetic in various neoplasms leading to an understanding of the molecular pathways participating in the biology of cancer. It is appropriate to consider cytogenetics as a fundamental adjunct to a variety of investigations underway, including basic and clinical research. For example, a rather simple cytogenetic analysis of mouse ES cells to determine ploidy prior to injections into blastulas leads to a greater success rate in establishing founders for knock-out and knock-in experiments. The primary chromosomal assignment of a gene by a FISH experiment may lead to correlation of a disease with that gene. Other cytogenetic studies may be important in establishing a diagnosis for correlation with clinical outcome. The advent of molecular probes for FISH analysis has facilitated cytogenetic studies in the mouse, and other model organisms and this Core aggressively implements such technologies.