Telomerase is the enzyme that extends the chromosome ends, thereby contributing 
to eukaryotic cell genome stability. Telomerase is expressed in the majority of 
cells that have an unlimited proliferation such as stem cells and cancer cells. 
The increased interest in telomerase in cancer research, challenged by the low 
cellular abundance of the enzyme, has led to the development of a reliable and 
at the same time very sensitive approach to detect telomerase activity. The 
telomeric repeat amplification protocol (TRAP) represents an easy and rapid 
method for detection of telomerase activity in cells. A non-telomeric TS primer 
is extended by telomerase in the first step followed by the PCR amplification of 
the products. The PCR step renders this protocol very sensitive to detect 
telomerase activity at the single cell level making it compatible with the 
analysis of tumor samples. When run on a polyacrylamide gel, the PCR product is 
a characteristic ladder of bands due to the repetitive nature of telomeric DNA 
sequence. The densitometric analysis of the ladder allows the TRAP assay to be 
used for comparative quantification of telomerase activity in different samples.