Levels of telomerase activity can be an indicator of the proliferative potential of somatic cells and may serve as a diagnostic biomarker of malignancy. Telomeric repeat amplification protocol (TRAP) is a fast and sensitive PCR-based assay for detection and measurement of telomerase activity. Since its introduction, the TRAP assay has been widely used in cancer and aging studies. It provides a powerful alternative to other in vitro telomerase detection methods, and has been combined with other molecular techniques to screen telomerase inhibitors, and to study human malignancy and other diseases associated with telomere or telomerase dysfunction.