In 1985, telomerase activity was identified in the macronuclei of the ciliate Tetrahymena and was found to add telomeric repeats onto telomeric oligonucleotide primers (1). The radiolabeled elongated products were detected easily as a 6-bp ladder on an electrophoresis gel. In 1989, using the same method, human telomerase activity was identified in a HeLa cell extract (2). However, the telomerase activity of human cells was very weak, and it was difficult to analyze the biochemical properties of telomerase or to investigate the significance of telomerase in various diseases, such as cancer. Therefore, we began to investigate a sensitive polymerase chain reaction (PCR)-based detection method for telomerase activity. Our goal was to develop a method that was not only versatile but also useful for biochemical analyzes, such as the measurement of the level of processing and the kinetics of telomerase.