Background: Differential methylation activity of the human rDNA in Alzheimer's disease (AD) patients has been demonstrated by classic cytogenetic tools. indicating a decrease in rRNA gene expression. Methylation of CpGs is an important epigenetic mechanism involved in gene expression repression of tandem repeating genes during ageing. Thus, rDNA specific methylation pattern could be involved in AD and be used as a marker of the disease or of its progression. Methods: The methylation pattern of three rDNA regions, including the promoter, 18S, and 28S, was investigated with the use of restriction endonucleases sensitive to methylation and Southern blotting, from DNA extracted from total peripheral blood cells of 28 AD patients and 28 elderly and Young controls. Results: We did not find a significant divergence in the methylation pattern of the Studied regions and in the relative amount of rDNA methylated copies among the individuals' groups. Conclusions: No differential methylation pattern of rDNA genes was observed in total peripheral blood cells in aged and AD subjects by the methodology used. (C) 2008 The Alzheimer's Association, All rights reserved.