The presence of Barr bodies was investigated in cells of a fibroblast culture, which consisted mainly of diploid cells with two X-chromosomes and triploid cells with three X-chromosomes in approximately equal numbers. Out of a total of 1000 cells, 487 cells contained a single Barr body and 64 contained two Barr bodies. By measuring the DNA contents of interphase nuclei in arbitrary values using an integrating mícrodensitometer it could be shown that some of the nuclei containing two Barr bodies were triploid, while the rest were more highly polyploid. It is concluded that for a given number of X-chromosomes, triploid cells may contain the same number of Barr bodies as diploid cells