The Trypan Blue Solution (0.4%) is a conventional cell staining method that can be used to evaluate cell viability through the dye exclusion test. This test is usually carried out when counting cells using a hemocytometer during routine subculture procedures. However, it can quickly and accurately determine cell viability at any time as needed. The dye exclusion test is based on the concept that living cells cannot take up impermeable dyes (such as Trypan Blue), while dead cells are permeable and can absorb the dye.