Among critically ill patients, opacification of a part or whole lung field on chest radiography may pose a challenge in the differential diagnosis of acute pulmonary pathologies (eg, pneumothorax, hemothorax, pleural effusion, atelectasis, and solid organ in thoracic cavity) and selection of treatment modalities. In cases in which clinical findings, history, and imaging studies are not conclusive, bedside ultrasonography may be invaluable in achieving a diagnosis. We present two cases in which portable ultrasonography at the bedside was critical to the diagnosis and subsequent management of the patient. (C) 2006 Elsevier Inc. All rights reserved.