The telomeres of somatic cells become shorter with individual aging. However, no significant change in subtelomeric methylation of somatic cells with aging has yet been reported. Telomere lengths of the peripheral blood cells of 148 normal Japanese were analyzed by Southern blotting using methylation-sensitive and -insensitive isoschizomers. With aging, long telomeres decrease and short telomeres increase, and the contents of the telomeres with methylated subtelomere increase in long telomeres, thus leading us to postulate that telomeres with less methylated subtelomeres tend to become shortened faster. A telomere length distribution analysis with methylation-sensitive and -insensitive isoschizomer seems to be a useful tool to assess the subtelomeric methylation status of the somatic cell population. The subtelomeric methylation of peripheral blood cells is also indicated to be an indicator for aging-associated genomic changes.