This article reviews the changes in bronchoalveolar lavage (BAL) cytology and cell differentials in some of the rarer interstitial lung diseases. In a few of these diseases BAL has a diagnostic value and can replace lung biopsy. In pulmonary Langerhans cell histiocytosis the characteristic diagnostic finding is an increase in CD1 + Langerhans cells greater than 4% of total cells. The sensitivity of this cutoff value is low because only approximately 50% of patients show this elevation. In pulmonary alveolar proteinosis, the sensitivity of a diagnostic BAL is almost 100%, and the characteristic finding of milky and turbid fluid on gross examination and the characteristic findings with acellular globules that stain pink with PAS (periodic-acid-Schiff), along with abnormal foamy macrophages and a characteristic dirty background obviates the need for lung biopsy. In diffuse alveolar hemorrhage, BAL is the method of choice to diagnose the alveolar bleeding by showing free red blood cells and hemosiderin-laden, iron-positive macrophages. The underlying disorder has to be identified by history and clinical and laboratory tests. In eosinophilic lung disease, the diagnosis can be made if the BAL cell differentials show 25% or more eosinophils. In collagen vascular disease-associated lung fibrosis, the precise role of BAL in assessment and monitoring disease remains unclear. In drug-induced interstitial lung disease BAL may support a certain clinical/pathological pattern of lung involvement and is helpful for exclusion of other diseases, such as malignancies with pulmonary metastasis, heart disease with pulmonary congestion, or infections. The same is true for radiation-induced lung injury.