Abstract P93-50, a 93-basepair (bp) repetitive DNA sequence from rats, was hybridized to transformed sublines of rat endothelial origin. The sequence hybridized at or near the centromeres of most but not all chromosomes in two transformed cell lines and three single-cell derived cultures. The hybridization signal was also frequently present at the telomeres. These cell lines have a highly aberrant karyotype including dicentric and multicentric chromosomes; however, even though this sequence labeled the centromere regions of some chromosomes, it did not hybridize with the telomere regions of the cell line XC, which rarely shows any dicentrics. Apparently, the telomere signals represent prematurely separating, inactive, terminal centromeres. The p93-50 sequence does not influence the timing of centromere separation, nor it is necessary for formation of heterochromatin.