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.