Within the past few years new staining techniques have been developed which have enabled the accurate identification of all the chromosomes in the human karyotype. Previously identification was based mainly on morphological criteria and to a lesser extent on autoradiographic techniques. The first of these new staining methods was introduced by Caspersson and his colleagues (1969, 1970, 1971) and involved staining of metaphase spreads with the fluorochrome quinacrine mustard and viewing the preparations under UV light. Chromosomes treated in this way show a pattern of cross striations or bands. Each pair of homologues has a characteristic banding pattern by which they can be readily identified. The main purpose of this study was to assess the usefulness of the fluoroescence technique as a routine laboratory procedure and if successful to apply it to various eroblems in human cytogenetics. The more readily available and less expensive fluorochrome quinacrine dihydrochioride was used here and it was found that the staining method was simple and gave constant and reproducible results. (Abstract shortened by ProQuest.).