Thymidine incorporation assay is the most common assay which utilizes a radioactive nucleoside, [³H]-Thymidine. In a typical thymidine incorporation assay cells are cultured a couple of days in the presence of a suitable stimulating agent (growth factor) and [³H]-Thymidine. During mitotic cell division (proliferation), [³H]-Thymidine incorporates into the new DNA that is synthesized. Scintillation counting (beta-counter) is used to measure the radioactivity in DNA recovered from the cells in order to determine the extent of cell division that has occurred in response to a test agent.