Antikinetochore antibodies from patients with the calcinosis, Raynaud's phenomenon, esophageal dismobility, sclerodactyly, telangiectasia-(CREST)-syndrome of scleroderma were used as immunofluorescent probes to discriminate between the presence and absence of kinetochores in minute chromosomes not previously seen by conventional banding methods. Double minute chromosomes (DM) consistently lack the antigenic component of the kinetochore, which is direct evidence for the fact that they do not have a centromere. Although somatically stable in malignant cell populations, DM are unable to attach to the mitotic spindle. Conversely, despite their structural similarity to DM, chromosome fragments and supernumerary marker chromosomes exhibit intensely fluorescing kinetochores and, thus, are subject to a precise anaphasic distribution.