Immunologic data obtained from bronchoalveolar lavage (BAL) is useful for both clinical and investigative purposes. Although lidocaine, used for local anesthesia, is present in BAL in up to 12 mmol concentration, its effects on immunologic tests are unclear. The results of our study show that lidocaine has profound effects on the results of functional studies of immuno-competent cells. Care should be taken to quantify, standardize, and limit the exposure of alveolar cells to lidocaine during bronchoscopy if such studies are to be performed. However, exposure of cells for 25 minutes or less to lidocaine solutions up to 12mmol in concentration does not affect a variety of immunologic tests of interest. At the same time, carefully controlled use of lidocaine in lavage solutions significantly increases the number of cells obtained for study.