Phytohaemagglutinin (PHA) is a plant-derived lectin primarily extracted from the red kidney bean, Phaseolus vulgaris. It is known for its ability to agglutinate red blood cells and stimulate cell division, making it a valuable tool in laboratory research, particularly in immunology and cell biology. PHA is often used in laboratory settings to activate T cells for studies on immune responses. Its properties allow researchers to investigate cellular mechanisms and develop applications in cancer research and vaccine development. However, it is important to handle PHA with care, as it can be toxic if ingested.