Pulmonary alveolar proteinosis(PAP) is a rare disease in which the alveolar spaces are filled with an eosinophilic, PAS-positive material, whereas the interstitial architecture of the lung usually remains unaffected. Although a definitive diagnosis is usually made by an open lung biopsy, bronchoalveolar lavage(BAL) cytology may play a decisive role in the diagnosis and therapy of these patients and may spare a patient a more invasive diagnostic procedure. The author presents a patient in whom BAL cytology specimen contained the characteristic globules of amorphous proteinaceous PAS-positive material accompanied by background of rare macrophages and inflammatory cells. Ultrastructural study using BAL specimen can confirm the diagnosis of PAP.