Telomeric repeat amplification protocol (TRAP) is now a conventional assay for detecting telomerase activity. However, this method presents problems owing to tedious quantification, radioisotopic handling and limited number of samples that can be examined each time. In order to alleviate these inconveniences, a novel telomerase TRAP-ELISA assay for human telomerase activity was developed. Telomerase TRAP-ELISA assay is a system based on the combination of PCR-ELISA with TRAP. It was used to detect telomerase activity in 293 cells and RNase-pretreated or heat-treated cells as control. Telomerase activity assayed by TRAP-ELISA was positive when the number of 293 cells examined was 10, 10(2), 10(3), and 10(4). The A(formerly called OD) value depended on the number of 293 cells used in the assay. Telomerase activity of RNase-pretreated or heat-treated cells, and human normal endothelial cell was negative. The result of telomerase TRAP-ELISA was available within one day and was handled without radioisotope. Telome