A viability assay is a laboratory technique used to determine the health and survival of cells in a sample. It assesses whether cells are alive, dead, or in a state of stress, often using dyes that can penetrate only dead cells. Common methods include the use of MTT, Trypan Blue, or Alamar Blue to quantify cell viability. These assays are crucial in various fields, including pharmaceutical research, cancer studies, and toxicology. By evaluating cell viability, researchers can gauge the effectiveness of drugs, the impact of environmental factors, or the overall health of cell cultures in experiments.