Human chromosomes terminate in a series of T2AG3 repeats, which, together with associated proteins, are essential for chromosome stability. In somatic cells, these sequences are known to be gradually lost through successive cells divisions; however, information about changes on specific chromosomes is not available. Individual telomeres could mediate important biological effects as was shown in yeast, in which loss of a single telomere results in cell-cycle arrest and chromosome loss. We now demonstrate by quantitative fluorescence in situ hybridization (Q-FISH; ref. 7) that the number of T2AG3 repeats on specific chromosome arms is very similar in different tissues from the same donor and varies only to some extent between donors. In all sixteen individuals studied, telomeres on chromosome 17p were shorter than the median telomere length--a finding confirmed by analysis of terminal restriction fragments from sorted chromosomes. These observations provide evidence of chromosome-specific factors regulating the number of T2AG3 repeats in individual telomeres and raise the possibility that the relatively short telomeres on chromosome 17p contribute to the frequent loss of 17p alleles in human cancers.