Bronchoalveolar lavage is a relatively new technique that is used to study the local cellular, biochemical and immunological changes occurring in the lower respiratory tract. The procedure involves instilling a fixed volume of saline into a lung segment after the flexible fibreoptic bronchoscope is wedged into a distal bronchus. The saline is aspirated back and can be used for microbiological and other studies. Recently, attempts have been made to standardise the procedure in children and obtain data on BAL cellular profile in healthy children. The main indications for BAL are diagnostic, particularly to diagnose unusual infections in immunocompromised children. It is also helpful in the diagnosis of a number on non infectious conditions, based on the cellular profile and other constituents. With the availability of new techniques like flow cytometry, analysis of lymphocyte and other cell subsets has become possible leading to a better understanding of the immunopathogenesis of various respiratory diseases.