The length of telomeres is believed to critically influence cellular aging processes and disease development. In order to reliably monitor telomere length and the corresponding cellular telomerase activity by optimized procedures, either based on flow cytometry or quantitative PCR technique, we here propose three commonly used cell lines, HEK293, K562 and TCL1301 as standards. In this contribution, efficient methods to determine mean telomere length of eukaryotic chromosomal DNA and determination of the corresponding telomeras activity are outlined. In particular, wide-range standard curves for a precise assessment of telomere length of genomic DNA by quantitative PCR technique are presented, measures, which greatly simplify the evaluation of respective functional roles of telomeres when studying biological processes such as disease progression and aging.