In this paper we considered the value of correctly performed bronchoalveolar lavage (BAL) in diagnosis of interstitial lung diseases and in assessment of the activity of pathological process. We indicated the conditions of exact interpretation of the results of BAL cytoimmunological examination, i.e. fine standard handling of BAL material, including its collection, elaboration and choice of lavage site, as well as regarding external (e.g. cigarette smoking) and internal additional factors. We described the influence of BAL fluid recovery and of the method of staining on obtained results. We emphasized routinely performed BAL to be the valuable diagnostic and research tool in pulmonology however, the method may have limited usefulness and unnecessarily burden the patient, if technical guidelines are not observed.