Confocal laser scanning microscopy (CLSM) is expected to provide new optical information different from conventional microscopy in cell biology. CLSM provides high contrast images, individual continuous cellular tomograms without slicing cells, and stereographs which are observed by three dimensional reconstruction. We study the localization of nuclear DNA stained with PI, tumor marker antigen CA-125 stained with FITC, and signals in fluorescence in situ hybridization (FISH) with alpha satellite pericentrometric DNA probe of chromosome 17 to discuss the possibility of its application to cell biology or clinical use. Some of the applications of CLSM including its structure and principle are reviewed.