Intensive hypermethylation of the p15^INK4B gene associated with the development of MDS. Changes of the methylation status of the p15^INK4B gene in patients no. 15, 26, and 30 are shown. Because the 2.8-kb band was intensified or the 2.2-kb band was faint compared with those at initial analysis in these patients, hypermethylation of the p15^INK4B gene may have progressed with the development of MDS.