Interphase cytogenetic analysis in the diagnosis and study of neoplastic disorders. Cytogenetic information usually is obtained through the direct analysis of chromosomes from cells arrested in metaphase. Recently, advances in molecular genetics have made it possible to acquire cytogenetic information through the study of interphase and terminally differentiated cells. By using chromosome-specific DNA probes or probes that are specific for certain chromosomal regions, and by employing techniques of in situ hybridization along with nonradioactive detection methods, it is now possible to detect numerical and structural chromosomal abnormalities from nonmetaphase cells. When used as an adjunct to conventional cytogenetic analysis or when used together with knowledge of established cytogenetic findings for a particular malignancy, this new technology can serve to broaden the scope and utility of cytogenetic analysis beyond the limits of the present metaphase-based technology. Interphase cytogenetic analysis has application to the diagnosis and study of neoplastic disorders and, thus, has particular importance in pathology. 