Bronchoalveolar lavage (BAL) is a simple technique commonly used in humans to sample the contents of the epithelial lining fluid and determine the cellular and molecular composition of the pulmonary airways. In murine models, BAL makes it possible to sample immunological and inflammatory cell populations; it is indispensable for studying cell influx in disease models of the airways such as asthma and COPD. Cell counts can be combined with methods such as ELISA, immunoblot, immunohistochemistry, quantitative polymerase chain reaction, and HPLC to assess such inflammatory components as cytokines, growth factors, analytes, and receptors expressed at the cell membrane. Performing BAL in a reproducible manner is a hallmark of airway research in the mouse. Several procedures may be implemented. This unit describes a basic, rapid, inexpensive, and highly reproducible procedure to collect BAL fluid and cells that can be counted efficiently and reproducibly. Curr. Protoc. Mouse Biol. 2:167‐175 © 2012 by John Wiley & Sons, Inc.