Bronchoalveolar lavage is a medical procedure used to collect samples of cells and fluid from the airways and lungs. This procedure involves inserting a bronchoscope into the airways and then flushing a small amount of saline into the lungs. The fluid that is then collected contains cells, proteins, and other substances that can be analyzed to diagnose various lung conditions, such as infections, inflammation, or cancer. Bronchoalveolar lavage is commonly used in research studies and in clinical practice to help diagnose and monitor lung diseases.