This study was carried out to compare the cell cycle distribution of rat thymocytes obtained by means of bromodeoxyuridine (BrdUrd) labelling of S-phase cells and the analysis of the S-phase fraction obtained according to the Vindelov et al. technique. The proportion of BrdUrd-labelled cells was analyzed in single cell suspensions of adult rat thymocytes after in vivo injection of BrdUrd and compared with the results obtained after measuring the cell DNA contents according to the Vindelov et al. method. The percentage of BrdUrd-positive cells was greater than the S-phase fraction obtained using the Vindelov et al. technique. By contrast, no major differences were observed between the percentage of BrdUrd-positive cells and the S-phase fraction obtained after analyzing the DNA histograms of the same data files with the RFIT mathematical model.

The elimination of trypsin treatment used in the Vindelov et al. method did not modify the results, while the use of DNA denaturation with 2N HC1 was shown to increase the percentage of S-phase cells calculated from DNA histograms independently of whether trypsin treatment was used or not, although the value of the S-phase fraction did not reach that obtained after BrdUrd labelling. Thus, important differences in the percentage of S-phase rat thymocytes of adult animals are observed when comparing BrdUrd-labelling and the Vindelov et al. technique; selective G0/G1 cell loss during washing and centrifugation steps performed after the DNA denaturation used for BrdUrd detection is the basis for these differences.